Maybe a scam, maybe genuine but a lot of these schemes tend to be useless. Also if they are paying you cash in hand for a service, you are technically self employed, so you will have to register with the vat man. So all that money you get will include VAT and your tax too. I would avoid it tbh. Any self employment oppurtunity should be encouraging you to be above board, this looks like it's not IMO.
http://www.mailingortyping.co.uk/faqs.html
Read that, their FAQS are not exactly encouraging honesty with tax, so be very, very wary.