Caught In The U.K. Filing Trap: How Defense Software Companies Can Lose Their U.S. Patent Strategy Overnight

Addressing the legal framework governing U.K. Government powers over privately developed defense technology.

Introduction

Here is a scenario that is more common than it should be. A U.K.-based defense software company has developed AI-enabled targeting or decision-support software. It has taken legal advice and been told—correctly—that the technology is unlikely to be patentable in the UK. The plan is therefore to file directly in the U.S., where the patent landscape for software is considerably more permissive. The company is ready to file. Then its lawyers point out something it had not considered: it cannot file in the U.S. without filing in the U.K. first (or obtaining a foreign filing licence). And that U.K. patent filing (or foreign filing licence application) may trigger a secrecy direction that blocks the very U.S. application it was intended to facilitate.

This is the U.K. filing trap. This article explains how it arises, why it catches defense software companies in particular, and what steps a company can take to protect itself.

Patenting software: the EPO and the U.S. compared

The threshold question—whether software is patentable at all—is answered very differently in the U.K. and the U.S., and that difference matters significantly for any company developing defense-related software.

In the U.K., computer programs are excluded from patentability as such under section 1(2)(c) Patents Act 1977 (PA 1977). For software to be patentable, it must make a "technical contribution" that goes beyond the normal functioning of a computer programme. The leading authority is Aerotel Ltd v Telkom Holdings Ltd; Re Macrossan's Application [2006] EWCA Civ 1371. In addition to this technical contribution requirement, the invention must be new, involve an inventive step, and be capable of industrial application.

There is no equivalent statutory exclusion of computer programmes under U.S law. While U.S. law requires that the invention not be an "abstract idea" and must demonstrate a technical improvement (Alice Corp Pty Ltd v CLS Bank International, 134 S. Ct. 2347 (2014)), the practical threshold for software patentability in the U.S. is substantially lower than in the U.K.

The difficulties in applying the U.K. test are well illustrated by the recent litigation in Comptroller-General of Patents, Designs and Trademarks v Emotional Perception AI Ltd. The technology was an artificial neural network (ANN) that made media file recommendations—a type of AI decision-making architecture with direct relevance to defense applications such as target classification, anomaly detection, and decision support. The IPO refused the application, holding that the ANN was a computer programme and therefore excluded. On appeal, the High Court held that it was not. The Court of Appeal reversed, holding that the training weights and biases of the ANN constituted a computer programme, and that the recommendation function was subjective and cognitive rather than technical—and therefore fell within the exclusion.

The Emotional Perception AI litigation underlines how uncertain and fact-sensitive U.K. software patentability remains, even for sophisticated AI architectures of precisely the type driving the current wave of defense innovation.

The U.K. first filing obligation

For a U.K. based defense software company, the divergence between U.K. and U.S. software patentability creates a clear commercial objective: file in the U.S., not the U.K. The problem is that it cannot do so without first satisfying an obligation that it may not have anticipated.

Section 23 PA 1977 prohibits any person resident in the U.K. from filing a patent application outside the U.K.—in the U.S. or any other jurisdiction—unless one of two conditions is satisfied. The first is that a patent application has been filed at the U.K. IPO for the same invention, and either the application has been published or at least 56 days have elapsed since filing without a secrecy direction having been imposed. The second is that the Comptroller has granted prior written authority to file abroad—commonly referred to as foreign filing clearance.

These are two separate procedures. Filing a U.K. patent application is a full application with all that entails—claims, description, drawings, and fees—and subjects the application to the IPO's automated security screening from the moment of filing. Applying for foreign filing clearance, by contrast, is a distinct application in which the applicant submits the technical details of the invention to the Comptroller specifically for the purpose of obtaining authority to file abroad without first filing a U.K. patent application.

The critical point—and the one that closes the trap—is that applying for foreign filing clearance triggers the same section 22 security scrutiny as filing a full U.K. application. The Comptroller reviews the technical content of the invention as part of assessing whether to grant clearance, and if the technology appears to fall within the section 22 categories, the Comptroller can refuse clearance and impose restrictions equivalent to a secrecy direction, preventing the foreign filing entirely. The company that believed it could avoid section 22 exposure by bypassing the U.K. application route encounters precisely that exposure at the clearance stage instead—and without the benefit of having a full U.K. application on file that could eventually proceed to grant if the direction is later revoked.

Filing abroad without satisfying one of the two conditions under section 23—without a U.K. application and without clearance—is a criminal offence under section 23(3) PA 1977. There is no exception for inventions that are unlikely to be patentable in the UK. A company that files in the U.S. first, reasoning that it has nothing to file in the U.K., is exposed to criminal liability regardless of the U.K. patentability position.

The practical consequence is that there is no route to U.S. patent protection for a U.K.-resident applicant in the defence software field that avoids interaction with the U.K. IPO's security screening process entirely. Both available routes—U.K. application and foreign filing clearance—subject the invention to section 22 scrutiny. Understanding this before any filing decision is made is therefore essential.

IP strategy: considerations for U.K. defense software companies

Companies in this position should address the following as part of their intellectual property strategy—and in all cases, should do so before any filing is made.

Assess secrecy direction risk before filing. Consult the published list of military technologies and material prejudicial to national security or public safety to assess whether your technology is likely to be screened in. Bear in mind that the full keyword list is classified and that the IPO operates cautiously; there is no guarantee that a precautionary direction will not be issued even for technology that does not obviously fall within the sensitive categories.

Consider splitting dual-use variants. Where a technology has genuine civilian as well as military applications, experienced patent counsel sometimes employ a dual-application strategy: filing two applications simultaneously, both claiming the same priority date, one of which is drafted with a specification focused exclusively on civilian applications and using no language that would trigger the IPO's security screening keywords, whilst a second application describes the same underlying technology with explicit reference to its defense applications. The civilian-focused application may have claims broad enough to cover military use in principle—the claims are not limited on their face to non-military applications—even though the specification addresses only civilian uses.

However, this strategy has significant limitations that should be understood before it is adopted. The screening system operates not only on military-use language but on the technical performance parameters disclosed in the specification—accuracy thresholds, frequency ranges, guidance capabilities, and similar characteristics. If the technology is inherently sensitive at the parameter level, a specification that avoids military language may nonetheless be flagged. Additionally, claims that go beyond what the specification describes risk challenge for lack of support. And two granted patents on the same invention with the same priority date would constitute double patenting. Pre-filing legal advice—from counsel familiar with both patent prosecution and the export control framework—is essential before this strategy is attempted.

Prepare a contingency plan for secrecy direction scenarios. The plan should address: application for consent to file abroad under section 23(1) PA 1977, identifying the trusted jurisdictions where consent is most likely (Five Eyes allies and selected NATO partners); financial projections accounting for delays in publication, commercialisation, R&D, and fundraising, noting that a secrecy direction can restrict not just publication but communication with any specified person or class of persons; and record-keeping of losses with a view to a potential compensation claim under section 24 PA 1977 if the application is ultimately refused or abandoned whilst the direction was in force.

Consider trade secret protection as an alternative or parallel strategy. Where the technology is likely to attract a direction of significant duration, and where the U.S. patent route is the primary commercial objective, trade secret protection—combined with robust contractual confidentiality obligations—may be more effective. Unlike a patent application, a trade secret does not require public disclosure and does not create a trigger event for the secrecy order regime. Careful thought is required, however, about how trade secret protection interacts with investor disclosure obligations and with open-source dependencies that are common in AI-enabled defense software (and with the PV security grading regime, which applies to unpatented technology in the same way as to patented technology, at least where a company enters the defense supply chain or seeks to exhibit or export its technology).

Key takeaways

• U.K. residents with military-related software inventions cannot file abroad without first filing at the U.K. IPO and waiting at least six weeks. Filing abroad first is a criminal offence.

• That mandatory U.K. filing triggers the IPO's security screening process, which may result in a secrecy direction that blocks the intended U.S. application.

• The screening obligation covers U.K. national applications, European patent applications filed at the UKIPO as receiving office, and PCT applications filed at the UKIPO as receiving office. It does not apply to applications entering the U.K. national phase after international publication has already taken place.

• The U.K. software patentability threshold is significantly higher than in the U.S., creating a particular tension for defense AI and software companies.

• Strategies to manage the risk include early legal assessment, dual-use splitting of applications, trade secret protection, and contingency planning—all before any filing is made.

Conclusion

The U.K. filing trap arises from the intersection of two well-established legal rules that are rarely considered together by companies focused on their U.S patent strategy. It is not a theoretical risk: it is a practical consequence of mandatory filing obligations that have no exception for technology that is unlikely to be granted a U.K. patent. Understanding this constraint and planning around it is an essential part of any defense-sector IP strategy for a U.K.-based company.

In our next article, we step away from the patent regime and consider a different mechanism by which the U.K Government asserts control over unpatented privately developed defense technology: Private-Venture (PV) Security Grading—a compliance obligation that many companies acquire without ever knowing they have signed up for it.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.