True. But for a lot of people they don't want to manage the additional overhead. Sure at £400/day could roughly equate to £100,000/yr but that's as optimistic as you can get (assuming you work 5 days a week and only take two weeks off a year). The reality could be much less if you take into account sick days and days you just were not able to sell. Some people would rather just have a sure bet even if its much less than they could potentially take home if they were on their own.