THIS IS NOT LEGAL ADVICE!
How long ago was the conviction?? In the UK there is a spent system that allows you to live you life as a normal person if you have been free of crime for a cetain period of time.
Everyone makes mistakes in life, you do not have to pay forever!!
I think for assalt it is around 5 to 7 years crime free, but that is a guesstimate!!
Beware though!!! The UK and USA are much alike when it comes to immigration! They can seem very stern and do not give way to igronace of the law!
May be worth seeking UK law adviser on this matter. I know of a lot of Travellers who have been turned away from the UK for a lot less.
Good Luck.
Mark