Windscreen wiper threaded bezel Amazon
 

Please can anyone advise how to remove an old worn threaded bezel that the wiper arm fixes on to so as to press home a new one?

Grinder? Dremel if you want to be a bit careful.

R;

"threaded bezel that the wiper arm fixes on" ...is unclear to me. The Bushing which Wiper Arm gets its drive from is splined externally:
https://www.sw-em.com/Wiper_Arm_Bush..._Bjorklund.jpg
...and internally:
https://www.sw-em.com/Wiper_Arm_missing_bushing.jpg
Source: https://www.sw-em.com/Wiper_Arm_and_Blade_Notes.htm
...you may be able to rig some sort of puller to provide the substantial removal force required to separate it from its Driveshaft. Otherwise, as Derek suggests, careful(!) grinding is an alternative.

Note also that removing the entire Wiper Mechanical Assembly from the vehicle is not too much of a job, and it would allow much more comfortable, and less risky working on the bench (where a more in-depth service on the rest of the components could also be done).

Cheers