Commenting on the defection of the Conservatives most senior MEP to the Liberal Democrats, George Lyon MEP said: “This defection is a coup for Nick Clegg and a calamity for David Cameron.

“Someone who can't lead a united party in Europe is certainly not fit to lead Britain in the EU.

“Like any group that keeps questionable company, the Conservatives will find sensible voices in their party moving away from the lunatic fringe where Cameron has exiled them.

“I welcome Mr McMillan-Scott to the Liberal Democrats and look forward to working with him in the European Parliament.”