Also based in the UK, and as far as I know you're right. To reiterate, speak to the a solicitor, but I've been told informally by several solicitor acquaintances they're usually unenforceable.
Unfortunately a lot of people in the uk take advice on employment from the same solicitor's who did their house legal work and come badly unstuck.
The Q is can could you afford to defend a claim on your IP - you wont get legal Aid
In that case you would have a serious professional negligence claim against the law firm and possibly the solicitor who gave you the advice.