WBAC bought 124,000 cars and increased revenues by 14% in the six months to September.
The business is part of BCA’s car buying division that also supplies vehicles to the auctions operation.
Car buying profits rose 6% to £12.4mln while auctions were 17% ahead at £55mln in the UK and by 23% to £15.8mln overseas.
Supply issues in the new car market sparked by the tighter emissions tests meant fewer ex-fleet vehicles coming onto the market which pushed up second hand prices, said Avril Palmer-Baunack, executive chairman.
The downside was lower revenues and profits in the services arm as the reduced number of fleet cars meant less refurbishment work.
Palmer-Baunack, who attracted fierce criticism in September for her £29mln bonus, said she expects the emissions disruption to continue into the second half but to diminish eventually as new procedures are established.
Interim sales overall rose by 22% to £1.43bn, while profits rose 31% to £45.7mln.
The interim dividend rises 15% to 3p.