The pictures snapped by a passerby show the mother-of-four with her leggings down and half naked Wain behind her.
The passengers, who asked not to be named, said: "I do not believe they were so brazen."
Witness added: "We have a five-year-old luckily not in the car. It was pretty disgusting."
However, rather than off to be ashamed of what they did, the lovers revealed that they are used to getting loving canal under the bridge, on the banks of the river, parks, fields hedgerows.
"We both have fish tanks keeping piranhas me and Lisa in a pair of turtles and we were on our way to see the fish," said Gavin.
"That we call a supermarket and bought a few bottles. It was a hot day and must have got the better of us booze. We are passing the telephone box and laughing and joking and I said to Lisa," Fancy a Quickie? "And obviously she is," he added.
"Gavin has a great body from all his boxing training and sometimes I can not help jumping on him -. If we are indoors or not," said Lisa.
Gavin and Lisa, who have been together for a year, lived not far from the phone box in Tamworth, Staffs.
Making love in a public place is a criminal offense and the local forces of Staffordshire Police have confirmed they are investigating the images to determine if they believe a crime has taken place.