Dire.
My landlord pays them to sort out my house if we get problems. Before christmas (around the 17th December) we had a problem with our electrics, British Gas messed us about. My landlord ended up coming up from Leceister to fix it himself. He got a call back off of them on January 19th saying they could get an engineer round in the next few days to fix it!
Then a couple weeks ago we had another problem with our boiler, it stopped producing hot water. My landlord phoned up British Gas, they said they'd send an engineer out the next day. I was in the house, ready to answer the door when the doorbell rang the next day.
It got to about 11am and I'd looked in the front door for some reason. There was a card there saying the engineer had tried to call at 10am but no one was home. He hadnt even rang the door bell or knocked. My room is next to the front door so I would have heard him knock... We had to put in for another callout and he came a couple days later, eventually fixed it the following week when the parts came.
My landlord has said he wont be renewing the policy with them in the future.