This is a vertmy stupid question but I've just moved into a house that's on prepayment gas & electric meters so I'm still figuring everything out. How long can I keep the key out of the meter whilst I go and top up? I have about £15 of credit on the electric meter already but basjcally, could I take it with me knowing I'll be making other stops or should I do a direct trip to the shop and get it put straight back in. TIA!