Found a new private tuition company called Student Tutor UK that uses only students rather than professional tutors. The benefit of this is paying only about £10/hour rather than £20 or £30+ with 'professionals'.

On their website (http://www.studenttutor.co.uk ) you can find local tutors by postcode. The lowest I've seen for GCSE Maths is £7.50 an hour. Quite good considering she even has a CRB check.

Haven't tried it myself yet, but hope this may be useful to other parents out there.