I’d ask to be employed as a contractor so you can claim the tax back off your expenses
For the record, you can do this as a permanent employee (i.e. claim tax relief on business/work expenses), you don’t need to be a contractor. Fill out a form, send it to HMRC, they’ll amend your PAYE code.
But, that aside, from all I’ve read on this thread I’d avoid the role like the plague. 20 days hols is far from the norm, not paying travel expenses is bobbins, and if I was ever told “we have people who would do this for less”, I’d let them.
EDIT – and having worked for three outsourcers; you are a profit generating number. The profit is the amount they can charge for you (read, how hard they can make you work) minus the amount they have to pay you. Obviously the incentive is to maximise the former and minimise the latter…