From what you quoted from your contract you're stuffed, in my uneducated opinion on employment law.
This could be, far from being a control issue it could be a simple practical measure.
If your version of IT involves climbing under over open desktops, into the bowls of the floor to get at network cabling, then it's actually a sensible idea.
It means if you damage your clothing it's a £10 polo shirt the company probably gets at a big discount anyway. As opposed to a £100 Ralph whoever shirt the company may have to cough up for.
The other thing to look at is why wear out your clothes when you can wear out theirs! Company provided clothing saves a fortune, although the last one I had was impractical for use outside work, and the hat wasn't very comfie either.
In terms of advise, do you have an employee assistance program? Many company's do now, and they will give you free legal advise, which is better than an internet forum when it comes to the full in's and out's of employment law.
I'm afraid I agree with the earlier comment, the internet isn't a great place to ask for advice on complex legal subjects. Yes, ask away if you've been caught speeding, or you want to know if someone talking your garden gnome is really theft, there are simplish answers to those from people who do know what they are talking about (along with a great deal of dross from those who don't!), but this sort of thing is a solicitor job.