Storing up trouble

Our client is having a garage and store built at his own home for his personal use. The costs are £58 000 and £52 000 respectively.

Two tradesmen have given separate quotes to do the jobs ie one quoted for the garage and the other for the store. Both say they are not VAT registered and will not be charging VAT on the projects.

My concern is that although each of these jobs individually does not go over the VAT threshold the tradesmen must do work elsewhere and could easily be over the threshold.

Is there anything that our client can do to safeguard himself in the event that the two tradesmen should have been VAT-registered?

Obviously our client does not want to subsequently be presented with a VAT invoice if it transpires that they should have charged it.

Alternatively have I somehow misunderstood matters and...