AX gt rear axle bearing. Is it easier to get a new axle ! as my garage claims for mot?

No the axle bearing is very simple to change

It is relatively common for the shell of the wheel bearing to seize in place in small citroen and peugot cars. When this is the case most garages change the back axle if they can get one easily as its usually the cheaper option.

For Citroen AX it is probably cheaper and easier to get a new car!!!

You can replace the bearings but it is not a nice job to do, also u may take the radius arm off only to find the axle tube is badly damaged as well. Even if u buy a new axle tube u need to take the radius arms off the old one & replace the bearings while it is in bits. If u check with a main dealer u may be able to buy a complete axle, not sure if u can though.

Personally on a car of that age i'd ring round some French car breakers, u may find one from a low mileage late model AX or the one from a Saxo or 106 may even fit (not sure about that though).