Any advice cant get my nut undone!

My 'mobile' mechanic who we use for routine work on the MG is having a real problem trying to undo the rear wheel bearing nut.. he has tried everything..

even standing on the 'snap on' tool... which actually broke!! Heated it up.. used lubricant.. used another more heavy duty snap on socket protected by a scaffold bar and still it wont budge. Is my only option now to maybe take it to a 'garage' with perhaps a more high powered air gun to see if they can loosen it?? he's been a mechanic for over 30yrs and never had a wheel bearing he cannot undo.. Thanks guys for your support.!!

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