Yes, I think there was something on Watchdog about this - they were taking on old boilers, doing the annual service and then saying when it failed they couldn't get the parts and quoting £2.5k for a new boiler. The boiler was actually on their 'no parts list', yet they accepted it, and serviced it (and charged for the free labour+parts cover) whilst it was on that list. Turned out, local plumbers depot had the part for less than £50. BG were 'nice' enough to refund the year's payments (rather than refund the £2.5k they conned the person out of, although they did get a new boiler out of it) but nothing more than that.
David