It would be nice to have 850 quid in savings, yet alone £85,000!
However, to try to answer your question, JennyJoan:
If a saver had £100,000 in a bank which went 'belly up', the Government would ensure that he/she got the limit of £85,000 back. The remaining £15,000 would be treated in the same way as any other debt owed by a firm which goes bust: The liquidator would call in all of the banks assets and share them out among the people to whom money was owed. For example, if the liquidator worked out that there was only enough money to pay back just 1p for every £1 which was owed, the depositor would get back just £150 out of the £15,000 which they'd paid in above the guarantee limit.