"Software you solely maintain" and "software you pay someone else for" are not the only two options. You may have heard of something called "open-source software", which is a way that the load of maintaining a program can be spread around the community of its users — like paying a vendor to maintain it, but you pay in code instead of money, and you still get to use it even if you don't pay. Ruby, for example, the language he wrote this in, is open-source software. Much of the internet is built with it.

There are probably other companies in England that also need to report expenses to accounting.