I'm, in the UK. My employment contract is quite specific on these things. The company owns any IP I produce, and I'm forbidden from working on side projects...

I'm, in the UK. My employment contract is quite specific on these things. The company owns any IP I produce, and I'm forbidden from working on side projects... without permission from my manager. So given permission (in writing) to start a project, it'd then be all mine. Agreeing these sorts of things prior to spending time/money on your own stuff should avoid most of these legal haggles.