UK Landlord Forum / Life

I have just taken over management again of one of my flats.I am using another different agent for tenant finding.The keys for the flat include a meter key.This was installed a couple of years ago by a tenant without my knowledge.I hate these meters.
The agent reported yesterday that the power ran out while doing viewing.There are £12 arrears,due to daily standing charges.
He told me to take said key to the corner shop to top-up,and also ring Eon to have the arrears cancelled.How I wish I had not done so.

Today I have spent a couple of hours on the phone,had to visit the flat to get information off the meter,and set up an account in my name,even though a new tenant will move in shortly.Oh,and they don't cancel arrears.Never thought they would.
Now the old key has to be changed for another at the corner shop.I will add enough credit to enable  tenant to settle in,but do I assume that they will then have to go through the whole rigmarole themselves? The old key just used to be passed by the agents to new tenants,but I gather the one I get will be invalid after I cancel my account with them?