[bacbilla]

That sounds like a disappointing attitude from their legal department, but if it's a big company I can see that they don't want to get into those sorts of discussions.

Only you will know the stakes and what you're willing to risk; most judges in the UK are fairly pro-employee and take a dim view of big corporations overreaching their rights (but please don't take this as absolute fact!). If you're not a senior employee and you're doing something like I mentioned in my previous comment (making a game in your spare time), I would personally not worry.

If it's your big idea for your future business and you want to work on it in evenings and weekends, then I would want to be rather more cautious.