Thanks your response
You can - however you will already be getting ALL expenses on the London property against your rental income so cannot have expenss twice -as I assume ALL the loan intetest. all the heating and lighting bills, all the insurance etc etc are claimed against the rents you receice, which leaves NIL for the business you run in the loft -
So you CANNOT have the same expenditure twice .... which is what you seem to be suggesting on the London property, for which you would not have any out of pocket expenses - as you claimit ALL against the rental income.
You can claim for Waled - as ou do incur additional expenditure for working from home - which is NOT already been claimed against another source of income.
To simplify this further - lets say you had to travel to London to carry out a repair on the London property - and this cost you £85 return and you thought - well whilst I am in London I see a new client
You cannot then claim the £85 against the rental income and also the business income - its either/or OR half from each as your visit had a duel purpose.
So it isnt so far as there is no system by which you can do this, its simple a fact that you already have amde the full claim against the rental income for the entire out of pocket expenses.
Hope that helps explain the position, but if you do incur extra expenses in the London property in the loft that are NOT incorporated within the rental income expenses claimed OR you have been making a private use adjustment to all the housing costs claimed against the rents - so have an availability - some of which are business (with your trade) then and only then would you have a considered claim for London