More tax revenue?
They haven't thought this through.
Sure, there will be some who just hike their rates to cover the extra tax, and there will be some who head abroad, but I reckon a lot will just go permie and at least have the comfort of sick pay and paid holidays, medical care, pension contributions etc.
Trouble is, permie work pays less, so there's less overall tax for HMRC.
Net result: Lower tax receipts, loss of skilled consultants, huge impact to workforce flexibility - inability for companies to hire on a project (ie revenue) basis - increasing risk all round.
The field I work in, Network Security, is comprised of about 80% freelance, 20% permie. Is that really an area where the government wants to reduce effectiveness?
Depending on how Brexit pans out for foreign workers (I should also mention that it's probably about 10-20% native Brits in my field as well, almost everyone I work with is from another country) we could end up with a perfect storm in which we red-tape ourselves to death :(