I don't know how helpful this is, especially because of difference in jurisdictions, but most US states would totally uphold this non-compete agreement.

In my jurisdiction for example, non-competes are valid if they (1) protect the employer's valid business interests, (2) do not impose undue hardship on the employee, (3) are not injurious to the public.

You may have an argument that the non-compete is unlimited in geographical scope, which is usually unfair, but again I don't know the exact nature of non-compete in the UK or even labor laws (majority US states are "at-will" employment, while in the UK I presume it's "right to work").

Sorry I can't be of more help