Hi Peter,
We do ours exactly as you do (except our labour is different) but as you know rrp for an mot is £50.00
We pay £30 or £32 for ours, depending on which station we use, so you can see the dilemma! £46.00 is very close to £50 but £30 is a far cry from it! So we have to make the retail price up to the £50 with either labour or a service charge.
Hope this explains our situation a little better Peter, as t is an awkward sitution for us.
Gunner.