Is the public house owned by you personally or by a limited company of which you are the director/shareholder?
Leave this with me while I draft my answer.
OK there is a mortgage
I'm afraid that you can only claim tax relief against your income for a capital loss you have suffered if that loss was from the disposal of shares in your own company or from the disposal of shares you subscribed for in qualifying trading companies (usually private companies) or through several different government approved investment schemes which are listed on page CGN13 here (boxes 12 to 15). All you can do is use the loss against capital gains you make in the same tax year as you incur the loss or in future tax years.
In order to register the loss with the tax office, you should set it out in your tax return. If you don't register the loss within four years of the end of the tax year in which it is incurred, you lose the right to use it.
I realise that this is not good news. Let me know if you have any further questions.