I would consider upgrading the first of your ‘serious challenges’ to a ‘very serious challenge’. The ‘cap’ in cap and trade w/r/t climate change can be arrived at scientifically. This government has already indicated its willingness to pander to exactly the sort of nationalist element that would frustrate any attempt to make a similarly dispassionate evaluation of the level of net migration required to stop this country sliding into the bog. As the right wing habitually fails to distinguish between economic migrants, refugees, non-caucasian British, and active terrorist cells, I would expect the ‘acceptable’ number of migrants to fluctuate wildly from year to year as May ineptly attempts to juggle the conflicting demands of the EDL and the Confederation of British Industry against a background of periodic racial panics. In so far as it marries the rigidity of C&C with the unpredictability of the market, you could be accused of combining the worst of both worlds.