Abbotyobs
Yes the £30ish should be taken at source but unfortunately some of the donuts at HMRC get it wrong - you should have a gross figure (with everything paid on it) and then a PAYEable figure (less Uniform Allowance, HTD, Dincome, Childcare Vouchers, etc...). You should only pay PAYE on the PAYEable figure. The difference for me last year, as a desert dodger for 2010, was about £4,500 between gross and PAYEable pay - which at 40% is £1,800 or at 20% £900 or somehwere inbetween.
I don't think you can "keep your head down" the Taxman already has the spotlight on you. Some of them might be donuts but they are very helpful if you can see and explain where they have gone wrong.
Best of luck
LJ