IANAL, but my understanding is that in order for the company to keep ownership of your designs, code, and other IP, you'd need to get some sort of consideration for that work. If you've been paid at least minimum wage then that counts as consideration, but if you haven't then you need to negotiate something reasonable in situations where a founder leaves the company before their 1-year cliff. 3% is fine, 0% wouldn't be fine though, unless again he had been getting paid. This is the reason why startups are always supposed to pay each founder at least minimum wage, even though normal employment laws usually don't require an owner of a business to pay themselves anything.
In the UK, founder agreements and similar with IP clauses are signed as deeds, not contracts. I understand the salient legal point is that a deed does not require consideration.
