Yep. I don't even need bespoke legal work; I'm happy if people just send an invoice with Commercial License as a line item and agree via email "Our Commercial License is the MIT license in the README and is available for $1,000 per year."

HNers often ask whether this is somehow dodgy, which it is not. Both of the tax agencies which care about my business give me virtually carte blanche to determine which products/services are necessary to keep the business running, subject to their standard regulations, and it is my considered judgment as a business owner that the software I use is necessary and that the amounts I pay are appropriate to the value received.

I've seen patio11 say things like this over the years, but hadn't connected the dots with this particular issue - genius. Certainly something we'll consider doing as a CYA against HMRC (or even our own bookkeeper who is rather strict with us).

You're not wrong, but it's also more complex than that. They could choose to apply "commerciality tests" which include things like whether you're paying over the odds or whether other forms of sponsorship would have a better commercial effect. https://www.gov.uk/hmrc-internal-manuals/business-income-man... is HMRC's own guidance to its tax inspectors on some of these points.

For example, if my company fancied donating £1000 a month to the curl project because we think it's a fantastic tool worth supporting (it is!) but we only use it in a handful of scripts, HMRC might give us some grief if it came up in an inspection. I dare say given the expected technical knowledge of the average tax inspector that a typical HN reader could prevail in such a challenge ;-)