In Oct 2020, HMRC changed the system so you get a whole year's reliefClaim tax relief for your job expenses GOV.UK
If your employer requires you to work at home, you can – and always have been able to – claim for increased costs due to working from home, eg, heating and electricity.
As per Martin's website: There are two ways to do this:
Employers can pay you £6 a week extra tax-free. Employers can give you an allowance up to this amount and what they give you is free from tax, so you get it all (to give you more, it will need to make special arrangements).
But right now – with many firms struggling – asking may be bad timing, so instead you can...
Claim tax relief on £6 a week. If your employer won't pay expenses for your extra costs due to necessary working from home, but you have them, then you can ask for the amount to be deducted from your taxable income. To make the process easy, HMRC says that claims in line with the employers' payment (ie, for £6 a week) will not need to justify that figure – meaning you won't need to keep receipts or prove information. Tax relief of £6 a week equates to a gain of £1.20 a week for a basic 20% rate taxpayer, £2.40 a week for a higher 40% rate taxpayer.