HMRC is permitting a claim for the entire year regardless of how many weeks of the year an employee has actually had to work from home.
Employees can claim a tax-free amount of £6 a week to cover the additional costs of working from home, and HMRC has set up an online portal to make the claim process easier. The figure to enter as the amount paid for 2020/21 is therefore £312 (52 weeks at £6). For 2020/21, this equates to tax relief of £62.40 for a basic rate taxpayer and double that for a higher rate taxpayer.
You cannot claim if your employer is reimbursing the £6 a week allowance or if you complete a self-assessment tax return. Relief is given by adjusting the 2020/21 PAYE coding, reducing PAYE over the remainder of the year.