Is your son taking the 11+ this year ?
If he is scoring that high why do you need a tutor? the passmark for Wirral is about 85% he is very close to that,and just needs practice over the timing.
I would recommened using the Tutors cd's on this site and their papers for practice ,if you buy these then I don't think you need to pay for a tutor,there are also lots of free demos on this site to give you an idea of how he's doing .
I would also look at the Wirral section on this site,lots of friendly people to help if you decide to tutor him yourself