It's a tricky situation, and I'm in two minds about it.
Whilst I appreciate minority communities "don't relate to the British legal system", if I went to the States, I wouldn't expect to cart Scots law with me; no, I would live under Federal and state law.
The same applies here; we already have three legal systems (English, Scottish, and Northern Irish). However, I acknowledge the English legal system allows the use of alternative systems of arbitration, opening up the possibility of Islamic sharia courts, and Jewish Beth Din.
There is a potential solution, then: let it should stay within those communities, exclusively, e.g. let Muslims deal with internal contracts under sharia law, provided it does not cause acts illegal under UK law. No hand-cutting, because the prosecution of Shoplifting would still be reserved to UK courts.
But, this is a very tricky area indeed -- one for politicians and law-makers, and certainly not one for clerics. It ends up like religio-cultural devolution for the justice system...