I work for a company in UK. This company is a branch of an american company. We have developed a software that resolves technical problems in an innovative way for the processing payments industry. I know software is not (generally) patentable in UK. The question is: can we file a patent for our software in US? The software has been developed in UK entirely.
Where an invention is created has no impact at all on the ability to be patented in the US. Nor does the nationality of the inventor or company. Under the Paris Convention, all (177) member countries must give people and companies from all other member countries the same substantial patent rights as they give their own nationals.
ARTICLE 2, paragraph (l) Nationals of any country of the Union shall, as regards the protection of industrial property, enjoy in all the other countries of the Union the advantages that their respective laws now grant, or may hereafter grant, to nationals ; all without prejudice to the rights specially provided for by this Convention. Consequently, they shall have the same protection as the latter, and the same legal remedy against any infringement of their rights, provided that the conditions and formalities imposed upon nationals are complied with.
In most places software based inventions are difficult to patent - sometimes impossible. It’s very complicated and a moving target at least in the US. I would suggest you consult with an experienced patent attorney/agent to determine the issues regarding the patentability of your invention in the US, the UK and elsewhere.