If you have a separate business premises, you can expense your rent costs.
If you work from your home premises, your rent expenses will most likely be captured as part of HMRC's flat rate (also known as ‘simplified expenses’), so how much you can expense will depend on how many hours you work from home.
If you're using your home as your small business premises, you can use HMRC's flat rate which varies, depending on how many hours you spend working from home:
HMRCs flat rate covers any rent and utilities. It does not cover phone or internet costs - you can expense the share of those that relates to your business.
It's also possible to determine a more specific share of any home costs that can be attributed to the business, however this can be complex.
For example, if you have a flat with 5 rooms and 1 of those rooms is used for work 8 hours a day, 5 days a week; you could estimate the share of bills as such:
Effective share: 0.20.330.71= 0.047.
0.047*100 gives us 4.7%.
As you can see, this is quite a small share. For most, it's much easier to go with the flat rate.
If you are struggling to determine costs to expense via the cost method, or would struggle to explain your rationale, it will be lower risk to use the flat rate instead.