Obviously oyur company will need to tread very carefully on this (no pun intended). Have a read through the case below, although not exactly your situation, it gives you an insight to DDA & health & safety, particularly with safety shoes. http://www.oldsquare.co.uk/pdf_cases/1200296.pdf

Rees, I expect that the employer will need to look at all alternatives before deciding on the release part or could prove costly!

Even without the legal issues I would have thought that the cost of advertising/interviewing/training new employee would outweigh an expensive pair of shoes.

Rees, I am not aware of any specific case law that might be helpful and tend to agree with others that you need to give this some careful consideration, before considering dismissal (on capability????). I wonder if you could elaborate on what the 'extremely high cost' is? Have you considered assistance from access to work?

I bet that a barrister /solicitor would cost U more to defend youe company [win or lose] for 1 hours court time than the shoes would cost U

The PPE Regs places an absolute duty on employers to provide PPE where there is a risk of personal exposure or harm, where the hazard has not been adequately controlled by other means, so there is no room for maneover there for the employer. S6 of the DDA Regs requires employers take reasonable steps in finding PPE suitable for the individual, which unlike the case I linked, you have found an alternative, albiet expensive in the employers eyes. As Ken say's, the fact alternative footwear has been found, your employer would certainly be disadvantaged in an ET. Are we talking about a small business, or a large blue chip company?