Deposit and Overdue Rent

Hi everyone! New Redditor here, but thought this might be a good place to get some advice :)

I've broken it down into a couple of queries:

So, I've requested for my deposit to be returned, and my landlord want to deduct nearly half the deposit amount for cleaning.

Now, the property (block of flats) is undergoing some fire safety remedial works, which is expected to take 18-24 months to complete (hence me moving), so this cleaning won't be able to happen until all the remedial works have been done.

So, my first question: Is it fair for the landlord to deduct this even though the cleaning isn't going to happen for almost two years?

The builders also needed access to the all the flats in the building from the 5th of Feb, and I had fully vacated, cleaned, and returned the keys on the 3rd Feb. In the hassle of moving, I had forgetten to cancel my Standing Order for the rent, so my rent payment which was due on the 1st Feb had already been sent to the landlord.

They have advised I am due to receive the overpaid rent, but they have only calculated this to be from the 12th Feb, as this is when the builders started the remedial works.

So, my second question: Is it right to only pay me the overdue rent from the 12th? Or should this be from the 3rd, when I vacated the property and returned the keys?

Thanks in advance :)