Oh, and most scummy landlords do wayyyyyy more dodgy stuff than just this one issue. If you really check through your tenancy agreement and everything that happened at the beginning of your tenancy, it's very common to find 3/4 totally illegal things that the landlord has done or included in the agreement. Obviously you tag that onto your case as well and make them severely regret ever disturbing your hornet's nest.
My landlord tried to charge me £125 for "removal costs" of a bicycle tyre that was there when we moved in lol. I took them to court for the £125, plus the £250 illegal admin fee they made me pay at the beginning of the tenancy, plus the £150 the made me pay to fix a washing machine at some point in the tenancy, plus interest on the extra deposit they asked for that they had no right to, plus interest on all of the above, plus my court costs.
Landlords break the law constantly because most people are desperate for housing and will never challenge it. And to be fair, it's stupid to challenge it if you're looking for a place. You're really going to say "nah, mr landlord, I'll reject your flat because you're asking for too much deposit legally?". No, you pay the deposit, you take the flat.... then you get it all back when you leave plus interest lol because you're the 1 in 100 people that does challenge it.
They tried to sting me for £125 as they probably do routinely with every tenant, but I'm not every tenant, so I walked away with close to £1k of their money and it was a piece of piss.