THE record of Members of Parliament who change political horses in midstream is not a distinguished one. Their moment of fame is usually brief and with only a very few exceptions they quickly disappear from sight. Carpetbagger was once the term used for those crossing the floor of the House of Commons and it was a description applied more than once to Winston Churchill as he moved around the parties throughout his career and ended somewhat uncomfortably in the bosom of the Conservatives in the late 1940s. Oswald Moseley was another itinerant politician, successively Conservative, Independent and Labour MP, in a hurry to achieve high office regardless of which party he served, until in desperation he founded the British Union of Fascists in the early 1930s. The move of Paul Marsden MP from Labour to the Liberal Democrats will not make much of entry in the annals of Parliament. His initial protest about Britain's military role in the anti-terrorism campaign was principled and even brave but he subsequently threw away the goodwill he had earned by increasingly shrill complaints about the way he was being bullied by the Labour parliamentary whips. There is nothing new about whips - of any party - pushing backbench MPs around and in the end Mr Marsden began to look more like a wimp than a man with a mission. It is rather surprising that Charles Kennedy wants him on the Lib Dem benches - any advantage will be shortlived because it is very unlikely that Mr Marsden will retain his Shrewsbury and Atcham seat for his new party at the next general election.