The only super power status symbol they have left to cling to is the nuclear deterrent, which could be sunk with Scottish independence. No wonder they're so desperate to cling on.
Brexit looks damahing enough for economically - which is not everything, true - but their way of withdrawing (bad grace and illegality and cavailer attitude to NI) could lost them their biggest allies, who (for first time in my lifetime) now have no particular interest in the UK sticking together.