Worth noting that in the UK it is pretty standard for your employer to pay for your lawyer (not their lawyer) to review your "compromise agreement" - there is a standard fee of £500 or so for this which a decent employment lawyer will be able to get a decent amount of work done even if their hourly rate is much higher.

I left my previous employer a couple of years ago and it ended up with a fair bit of negotiation and it was all covered under the standard fee. The particularly nice thing is that they bill your employer, not you!