Owing to a difference in the exchange rate authorised by Inland Revenur and the actual rate applied by the bank, I am holding a nominal large sum in the accounts. How do I reduce this figure to agree
Answers
I'm sorry but the question isn't clear.
Your bank balance is in local currency (I'm assuming £, but it really doesn't matter).
If your transactions in and out of that account are in the local currency, then exchange rate changes has no effect.
If those same transactions are of different currencies, then every movement would be adjusted by the bank upon settlement of funds.
I.e, I send you $100USD to your £ account. If it cleared today, strictly speaking (not including bank fees, etc.) you'd received £80.04. You would debit your cash account the £80.04.
However, if that payment was against an invoice made to me for £82.00, then you would have an FX loss (or bank charge) of £1.96.
Why you are keeping large sums in the account doesn't make sense.