How to advise HMRC of issue/estimation?

I have a client who had poor bookeeping systems in place and brought in a bookeeper towards the end of the year which i am now doing the accounts for (i can see improvements in the bookeeping for the final quarter).

Unfortunately the company had a fire and practically everything was destroyed. I was sceptical at first and so obtained fire reports, photos of the damage and also evidenced physcial invoices burnt/smoke damaged.

Now doing the accounts, there is a high level of uncertainty in the figures and given the lack of physical invoices it is near impossible to correctly identify the errors. The bookeeper has obtained duplicate copies where possible but for the period prior to the bookkeeper coming on board is proving near impossible as the record keeping was so bad. This a Limited Company - predominantly cash based business.

So is there anywhere i can tick/advise HMRC that the accounts figures are estimated/have potential errors and the reason why?

I have approached the accounts starting initially from the bank side (resulting in VAT being underpaid for the first 3 quarters) and the client will report this and a vat correction error. So in that instance i am satisfied that the client is co-operating and reporting any errors that we can identify given the lack of documentation and evidence and piecing together as best we can. The accounts figures have been prepared using enquries and the evidence available to us so in that respect nothing has actually been estimated but there is high risk of error as the client has made assumptions i.e. payments from the bank being expenses.

Any other recommedations? Note to the accounts identifying the issue of the fire and lack of documents. MLR to be on the safe side.

Many thanks in advance