Definitely seek professional advice. Obvious ones I can think of:
- Pay off mortgage!
- Look at fixed deposit accounts,
- Britannica have a 7% 12 month account at the moment, it's not instant access but I imagine with your other accounts you wont need access to this also.
- Read up on the compensation scheme, it varies country to country, over here it's called the Depositors Compensation Scheme, I believe in England it is similar, fortunately a professional should be able to advise you on the situation on the UK.
Finally, take advise from other people, on the internet etc as to what Independent financial advisor to speak to, ensure they don't have alterior motives as they may have a product of their own they want to sell. Cheaper isn't always better. And for what its worth, I'd stick 30k in premium bonds!