Someone has probably overtightened the plug and they have visions of stripped threads or a broken bolt, and they don't want the hassle, possibly they plug is chewed or shows signs of abuse.

Choice is yours, main dealer or a competent indy or have ago yourself (buy new plug first), if the threads strip out a good indy might put a helicoil in for you, main dealer will probably fit a new sump.

Sounds like they were prety incompetent. Should think almost every garage has come accross a rounded off sump plug at some time. A competent garage should have it out in five minutes. Worst case scenario is that they will have to drill it out & fit a hellicoil insert & new plug, About 1/2 hours work, if that.

Well, an obvious temporary workaround would be to go somewhere that uses one of those suction devices that removes the old oil via the dipstick tube. It's entirely possible that it's been done this way in the past (I believe it's the norm with dealer servicing these days) and that the sump plug has not been removed for some considerable time, which may well be why it's stuck.

Longer term, shifting the stuck plug is going to be a pain. If it's really well jammed, it's quite possible to strip the threads or thoroughly round the end of the plug[1] even when care is used, which will mean removing the sump (and potentially replacing it) to solve the problem.

[1] If those lads really are like Kwik Fit, it's probably well rounded by now......