I don't think you have a very nice landlord! I have a tenant who phoned me yesterday morning to say the shower wasn't working...it's a gravity fed one, with a booster pump. Had to get a new one and fit it...she's entitled to a shower, imho.
£170 for a pump...I am going to take this up with Salamander, as the "old" one was installed only 18 months ago.
Anyway, I digress...
In Scotland, the penalty for failing to lodge the deposit with an approved "scheme" is a fine of up to 3 times the monthly rent. I suspect, as Vortigern posted, you have a similar recourse in England, and you should pursue that regardless of how you resolve the current issue with the socket. Either use that as a threat to the landlord, or just do it afterwards anyway. These people should be punished!