The 1707 Act of Union provides that no Scottish case can be heard in an English court. It also removed Scotland’s parliament, but left it its judicial independence. The Faculty of Advocates, the equivalent of the Bar Council in England and Wales, says the supreme court would be unlawful and unconstitutional.
Apparently the Act of Union is entrenched, so it should not be possible for it to be amended (but it must have been an amendment when Scotland was given a parliament). That is one question. Another is, why would the supreme court be an ‘English’ court? It would be for the whole of the UK. And another: how is it that some Scottish appeals (in civil matters) go to the House of Lords?
In fact, the Herald article suggests that the main difficulty is with the proposals for a supreme court in their present form. There have always been one or two Scottish law lords, and similar provisions need to be made for a UK supreme court (if there ever is one). And perhaps the court is too closely integrated into the system of English and Welsh courts for the Scots to accept.