I could be wrong, but would not surprise me in the slighest if this was via agency umbrella operation, the deductions will come down faster than Niagara Falls, 2 lots of NI - employer & employee, payroll fee, processing fee, rolled-up holiday pay, just to name a few.
All this £20 an hour stuff I suspect will look a lot less exciting once deductions are taken.
Although I’m perfectly happy to be proved wrong.