In my research among MPs covering over a hundred defections and a span of a century, just three resigned their seats on defecting from the Liberals to Labour. Two - Joseph Kenworthy and William Jowitt - won back their seats under their new party colours. The third, William Wedgwood Benn (father of Tony Benn), resigned his seat and declined to stand again in the same constituency. He was elected as a Labour MP for a different constituency the following year. (His fascinating career will be the subject of my next biography.)
Dick Taverne who resigned his Lincoln seat on leaving the Labour Party in 1972, was re-elected the following year as an independent Democratic Labour MP, presaging the formation of the Social Democratic Party (SDP) in 1981. When 28 Labour MPs defected to join the SDP, only one - Bruce Douglas-Mann – resigned and fought a by-election. He lost.
None of the recent defectors from the Conservatives to Labour – Quentin Davies, Alan Howarth, Peter Temple-Morris, Robert Jackson or Shaun Woodward – resigned his seat when he defected, nor did Emma Nicholson or Peter Thurnham who defected from the Conservatives to the Liberal Democrats.
History shows that very few politicians have been willing to take the risk of resigning their seat on changing parties, but of the few bold enough to do so, most won their seats back.