Not many self employed tradesman here would be VAT registered. The trades i notice using old estate cars do not carry materials as they are delivered to sites. My 3 Nephews who run an electrical contractors business are all self employed so none of them get to the income where Vat registration is needed. Back in the 70s it was a VAT company when i also worked for it but my brother opted out and stopped employing staff. The 3 now working use VW T5 people carriers with black side glass as the van robbers just think its a camper without tools inside. When they did use vans, one had a side door peeled off in the night and tools stolen.
So many 1 man band site workers just have the 1 car that is their family transport so the old estate cars are ideal.
Most plumbers and electricians will use a van due to so many types of fittings but even those materials can be delivered within 1 or 2 hours locally.
One local builder who worked until he died at 74 used a Shogun which was really tatty. Very wealthy man and his other car was a 70s E type. Owned many properties in his Wifes name so no Vat for him just jobbing around bricklaying.