If you don't think the bank is likely to go bust in the foreseeable future, you could just ignore it – especially if your mother is not much above the protected limit and is paying for care.
On the other hand, £85,000+ is a lot of money to be sitting around doing nothing, so if she doesn't need the money urgently you could invest it. Good advice from
@nitram above, but a market-based fund would do better than a bank or building society.
The only difficulty with the latter is that as attorneys you should probably take professional financial advice first, and the adviser will want to know your mother's attitude to risk. Try to find someone who'll work for a small flat fee rather than the usual 0.5%+ per year for doing essentially nothing.