HMRC advise that you should not delay sending in your tax return just because you do not have all the information you need. If you feel that there may be the possibility of recovering the missing details, then you should submit your return with provisional figures. You should advise HMRC when you believe that the missing information will be available and you must then ensure that revised figures are submitted to HMRC as soon as possible.
If you feel that the records are unlikely to be recovered, you should submit estimates for the period which is missing. These must be reasonable estimates and you should be aware that HMRC obviously reserve the right to raise an enquiry on your return to ensure that your estimates are reasonable, consistent with similar trades and in line with previous years' figures. Using estimates based on periods where you do have records and receipts is the most suitable procedure to obtain accurate figures and duplicate bank and credit card statemnts can be obtained to help to substatiate those figures.
When you are running a business, we would urge you to ensure that paper records are kept in secure storage and that electronic records are backed up regularly, to help prevent problems such as this occurring.