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 that you can recover the information then you should submit your return with provisional figures, and advise tMRC when you expect to be able to file actual figures. You must ensure that figures you provided are reasonable and take account of any information that is available for the same period.
If you feel that the records are unlikely to be recovered you should submit estimates for the period which is missing. Once again these need to be reliable estimates, and you should be aware that HMRC obviously reserve the right to investigate and ensure the figures are reasonable and consistent with similar trades and previous years figures. Using estimates based on periods where you do have records and receipts is the most suitable procedure to obtain accurate figures.
Business clients should really be advised to ensure suitable back up procedures are in place to prevent problems such as this occurring. Duplicate bank statements can always be obtained as a last resort to substantiate reported figures.