I need pocket money.
You don't just need pocket money, you need survival money. I am not sure if finding a writing job and starting out without any experience would be beneficial to you in this case. Your bills may pile up faster than the company can pay you and, you may not earn enough to cover your bills at the start.
I would like to know if it is profitable enough to work for UK companies, and what kind of pay I should expect.
It would be, provided you work for a legitimate writing company out of the UK and not for one of the posers who will just enslave you then dock your pay till almost nothing is left.
Do you manage to live off your freelance work alone?
It takes some time to build a reliable client base and income flow but yet, you can actually live off freelance writing work and life comfortably. Debts will be paid with some left over to enjoy yourself sometimes.