I was surprised by the vat angle too, however 2 different companies I have worked for, have had the same rules applied to them.
The accountants tell us if 50% of the turnover is MoTs then only 50% of the vat can be reclaimed.
I have noted when ordering through the system, the consumables do not have a vat breakdown, nor is there a vat number supplied.
I've found a cheaper source for the consumables so will obviously use them rather than SBS.
Another anomaly, if another garage uses us for MoTs and gets a trade price, but charges the customer full price for the MoT, they are liable for vat on the difference.