I would recommend doing your own research on this one. Contractor UK forums are worth reading -
http://contractoruk.comContracting in the UK used to be pretty good. These days things have changed a lot with further IR35 crackdowns.
I've investigated this a few times personally over the years and am a permanent employee still. Admittedly a few rungs up the corporate ladder these days, but contracting isn't the gravy train it used to be.