Then the President's plane crash lands in London right?
They should do a trial run of what it would be like for Britain to leave the EU. For one year the UK could make no contributions towards the EU and the EU no contributions towards the UK. Lock all the borders down and allow no-one to leave or enter the UK. Institute passport checks on the Northern Ireland/Ireland border. Destroy any sign or building with an EU flag on it inside the UK.
That'd be fun to watch.