There are four overriding requirements for a patent to be granted under United Kingdom patent law. Firstly, there must have been an invention. That invention must be novel, inventive and susceptible of industrial application. (See Patentability.)

Patent laws in the UK and throughout Europe specify a non-exhaustive list of excluded things that are not regarded as inventions to the extent that a patent application relates to the excluded thing as such. This list includes programs for computers.

Despite this, the United Kingdom Intellectual Property Office (UKIPO) regularly grants patents to inventions that are partly or wholly implemented in software. The extent to which this should be done under the current law and the approach to be used in assessing whether a patent application describes an invention has been settled by the Court of Appeal. The UK approach is quite different from that of the European Patent Office (EPO), although "there should be no significant difference in result."^[1]

Globally, the extent to which patent law should allow the granting of patents involving software (often referred to as "software patents") is controversial and also hotly debated (see Software patent debate).

Although it is an implicit requirement of Section 1(1) of the UK Patent Act (1977) that patents should only be granted for inventions, "invention" is not defined anywhere in the Act.

Instead, Section 1(2) Patents Act provides a non-exhaustive list of "things" that are not treated as inventions. Included in this list is "a program for a computer". However, these things are only prevented from being treated as inventions "to the extent that a patent or application for a patent relates to that thing as such".

Article 52(2) of the European Patent Convention (EPC)^[2] includes a slightly different list of non-inventions, although "programs for computers" are present. Article 52(3) EPC then states that patentability for the identified subject matter or activities is excluded "only to the extent to which a European patent application or European patent relates to such subject-matter or activities as such".

The wording of the Patents Act is slightly different from Article 52 EPC, but the UK Courts have taken the view that since the purpose of Section 1 of the Patents Act was to transpose the requirements of Article 52 EPC into UK law, any differences between the EPC and the Patents Act should be ignored. The text of the EPC itself should therefore be regarded as definitive.

Other things that are not regarded as inventions include mathematical methods, and schemes, rules and methods for performing mental acts, playing games or doing business. These additional excluded categories often overlap with the exclusion of computer programs since they may be put into practice using a computer.

On 2 November 2006, following the judgment in Aerotel v Telco and Macrossan's Application, the UKIPO issued a Practice Note announcing an immediate change in the way patent examiners will assess whether inventions relate to patentable subject matter.^[15] This practice is considered to be a restrictive interpretation of the judgment by patent attorneys.^[11][16]

One aspect of the practice change was a reversal in the UKIPO practice concerning computer program claims. For several years previously, the UKIPO had allowed claims directed to a computer program if the method performed by the computer program was itself patentable. In light of the first step of the Aerotel/Macrossan four-step test, to construe the claim, the UKIPO decided that claims to a computer program were not a permissible form of claim even if the underlying method was found to be patentable.^[15]

This practice remained in place until 7 February 2008 when, following the judgment in Astron Clinica and others' Applications,^[17] the UKIPO issued a new Practice Note stating that they would return to their previous practice of permitting claims to computer programs if claims to a method performed by running a suitably programmed computer or to a computer programmed to carry out the method were themselves allowable.^[18] This change affirmed the established practice of considering the substance of the invention over the particular way it was claimed but it was not thought that it would cause a material change in the subject matter which would be deemed patentable by the UKIPO.^[16][18]

Patents granted by the European Patent Office (EPO) may be brought into effect in the UK once certain formal requirements have been met.^{[citation needed]} As soon as a European patent is granted (provided that no opposition is filed), then final authority to interpret Article 52(2) and (3) EPC rests with each national jurisdiction and any person may apply to the UKIPO or the UK courts to have a patent granted by the EPO revoked in the UK.

There is to date no supranational European system for patent litigation, so the courts of each EPC Contracting State retain the final say. They vary to some extent from one to another as to just how far the exclusion should extend.

Compared to the EPO, the UKIPO have consistently taken a very different approach when deciding whether or not to grant patents involving software. This has sometimes drawn criticism from those advocating the need for harmony across Europe. (See Proposed directive on the patentability of computer-implemented inventions).

The most important difference between the two offices is that the EPO will in general accept that any patent application relating to a computer-implemented method is "an invention", whereas the UKPO will reject an application on the basis that it does not describe "an invention" if the only contribution provided by the inventor is a computer program. The EPO instead only consider technical features when assessing the presence or otherwise of an inventive step and will therefore normally reject the trivial computer-implementation of a non-technical method as lacking an inventive step. The UKPO, in contrast, consider any feature, technical or not, as being capable of contributing to an inventive step. (See Software patents under the European Patent Convention, which discusses the evolving position and practice of the EPO on this issue.)

Thus, for example, a patent application describing a new computer chip used to implement a faster method for calculating square-roots was rejected as not being an invention in the UK (Gale's Application), but would probably be deemed an invention in principle by the EPO. The EPO would instead consider whether the new method of solving square roots provided a technical solution to a technical problem and would only grant the application if such a solution were inventive.

It was noted by the Court of Appeal in Aerotel and Macrossan that using the reasoning of most of the EPO case law (such as T 258/03 – Hitachi) would result in the same final conclusion as the "contribution" approach. However, the reasoning in a particular Microsoft case^[19] was held up as being flawed. The UKPO have also expressed the opinion that the end result would normally be the same.^[15] This is disputed by groups such as the Foundation for a Free Information Infrastructure who consider that the EPO is consistently granting patents that would be refused by the courts in the UK and elsewhere in Europe.^[20]

• Software patent
• Software patents under the European Patent Convention
• List of UK judgments relating to excluded subject matter