Replace extradition with UK based trials

I suspect this needs more thought (I'm guessing renegotiating extradition treaties is unlikely to be simple!) but I think the current system is unbalanced. The burden should be firmly on the prosecuting country, which has far larger resources at its disposal than the average defendant who, after all, is innocent until proven guilty.
Trying people in the UK seemed like a good starting point, especially given the nature of some crimes that have caused problems (committed in the UK, or where there are doubts about fair trials abroad, potential for onward extradition, etc.). The intention is, if the details can be made to work, to end up with a much quicker process (fewer fights against extradition) and one that doesn't unduly punish anyone before they are convicted.
Any thoughts?
Cheers, James