Direct Answer
HMRC does not recognize accounting depreciation for tax purposes. You must add back all depreciation expenses in your tax computation to arrive at taxable profit, and then deduct HMRC-approved Capital Allowances (like the Annual Investment Allowance).
The Difference Between Accounting and Tax
Your P&L might show a £10,000 depreciation expense for a van, calculated over 5 years. HMRC ignores this.
Capital Allowances
Instead, HMRC offers the Annual Investment Allowance (AIA) or First Year Allowances, which often allow you to deduct 100% of the asset's cost in the year of purchase. Therefore, a pre-filing review must physically verify the asset purchase invoices in the bank statement, classify them into appropriate Capital Allowance pools (Main Pool vs Special Rate Pool), and entirely reverse the P&L depreciation.