However, they are entirely within their rights to replace them as their candidate at the next election if they have left the party.

Right now, there is a debate as to whether the local party have the right to remove that endorsement from a sitting MP who hasn't left the party, but whose behaviour or political philosophy the membership deem  no longer acceptable.  

However, the national party do retain that right. Simon Danczuk, MP for Rochdale, will be removed by the national party at the next election

keep to the Fen Causeway