Hospice chief executive Toby Porter said he cast his vote in Oxford at 7.25am, and the normal polling station was “up and running” by 7.30am.
He said around a dozen people voted in the car before the centre at the Oxford Centre for Mission Studies was opened.
“We found it funny. Everyone was enjoying the novelty,” said Mr Porter, who was on his way to work in the West Midlands where he has recently helped secure the future of the children’s hospice in Walsall.
Laura Lock, deputy chief executive of the Association of Electoral Administrators, said some polling stations in cars are seen at each election. She said: “All polling station staff are trained on how to set up temporary polling stations for cases just like this.
“Unfortunately we do find key holders oversleeping, so every election we see a handful of polling stations in cars until access to the building can be sorted.”
A spokesman for Oxford City Council said: “The keyholder overslept and for a short time at 7am electors were voting using the POs’ (presiding officers) cars.
“This is standard procedure when a station building isn’t open on time and part of the training we give them.
“The key is that ballot papers are ready to be issued at 7am, wherever that may be. The building was open within 15 minutes.”
Polling stations had to make several adaptations to allow voting to go ahead within the restrictions imposed by the coronavirus pandemic.
That meant keeping polling booths further way from each other and asking voters to bring their own pencil when possible.
Long queues stretched out of the doors of some polling stations because queuing was now being allowed inside.
Voters were also asked in many stations to enter the room one at a time, even if they had travelled their as a couple or family bubble. The queue at the station in Mount Road, Penn, Wolverhampton, wound its way through the grounds of St Aidans Church and up the road as people waited to vote in local, police and mayoral elections. First-time voter Maisie Drew, 18, of Penn, said: “It was cold in the queue but everything was well organised and good humoured.”