Registrations in the UK fell 1.6 percent to 140,945 in October, according to the SMMT industry association.
A lockdown in Wales to reduce COVID-19 infections accounted for more than half of the overall UK decline, the SMMT said in a statement on Thursday.
The Welsh government's intensifying efforts to slow the spread of the coronavirus forced showrooms in the country to close on Oct. 23. There were 26 percent fewer registrations in Wales during the month, the SMMT said.
Subdued activity from businesses across the UK also contributed the the month’s drop, with about 2,500 fewer vehicles joining larger fleets than in October last year, while private registrations saw a modest increase of 0.4 percent, the SMMT said.
England followed Wales on Thursday in introducing a lockdown to curb the pandemic. Showrooms in England will close to walk-in customers until Dec. 2, but they will be able to hand over cars ordered online in a so-called "click and collect" service.
The SMMT hopes "click and collect" will help to avoid a repeat of a disastrous spring when sales plunged by 89 percent in May and 97 percent in April during the British government's previous lockdown.
The association warned that online sales cannot offset the loss of customers resulting from the closure of showrooms because most car purchases are still done at a dealership.