Surely there's a tad more at stake than a narrow self-interest issue?
This upcoming General Election has the potential to alter the course of the UK for a generation or more. Trying to boil it down to a narrow special interest to attract the attention of a voting bloc seems at best a bit disingenuous.
FWIW -- Being an individual sub-contractor has always been a pact with the Devil. You get to pick how much you work, where you work and effectively how much you're paid with the rate sounding incredibly attractive to normal working stiffs. But it is not real money, any more than the amount taken per day in the cash register of a corner store is representative of the income of that store. So its the trade off -- freedom and flexibility comes with the extra hassles of tax, having to make provision for unemployment, sick leave, vacation and the like. Like the corner store when you run the real numbers you might find that the actual hourly rate is quite miserable. Also like the corner store, if you don't run the place like a business you're going to eventually be eaten alive by the taxman.
The fact that modern employers have extended contract work to what are regular employees being paid regular wages is a scandal, its a way of pocketing the excess cost of employment by shifting those costs to people who either don't know any better or have little to no choice, its either that or starve (a choice that we thought we'd seen the back of after WW2). So -- look at the big picture and choose your representatives accordingly. You may not get another chance.