Bike shop.
I'm not mechanically gifted. I live in a 2nd floor flat, with no space in the flat to fettle, and poor facilities outside. I have done a one-day maintenance course, but it's like anything, if you don't do the stuff regularly, you forget it. I clean and lube the bike regularly but that's about it. I'd rather pay someone to do it right than risk doing it wrong myself and have a vital bit fall off when I'm in traffic.
I'm still paying for the bike on the bike-to-work scheme, but I'm also getting a lot of mileage, so in the months that the mileage exceeds what I'm paying, I put the difference into a separate account and use it to pay for bike stuff.