Not wishing to give potentially "illegal/unethical" advice. It would appear that based on these article's:

http://www.wired.co.uk/news/archive/2010-07/28/investigation-is-it-legal-to-jailbreak-a-uk-iphone

http://www.pcadvisor.co.uk/how-to/apple/3344366/how-jailbreak-your-iphone/

You're OK with regards to legality jailbreaking your iphone in the UK, as long as you're not infringing copyright.

Last time I looked and I'm sure you know this already but jailbreaking will set a default root password that should be changed.

There also maybe issues with T&C's for both the phone and the app, but you'll need to review these yourself.

A quick google for "iphone software bypass jail break check" shows that xCon may do the trick. Although some people have mentioned it won't work for all apps.

All in all a long way for me to say xCon, but for my conscience I needed to write the above. 

Thanks for the info and its all being used to test an app for another company just want try something thats all.