The Witchford Road Service Station in Ely, Cambridgeshire, has been chosen to conduct the trial, which will see M&S Simply Food sold in a forecourt supplied but not owned by BP for the first time.
The companies could not confirm exactly when the trial would begin or how long it would last, but development of the site is planned to start early next year and the store is expected to open for business in the M&S format in the first half of 2009.
The project was still at an early stage, James told The Grocer. Details of the ranges and lines to be stocked were also still being fleshed out, he added.
"There's still an incredible amount to bottom out. We've got to have meetings with BP in the near future, there's a lot to deal with and a lot to put together."
James, whose company James Graven & Sons owns five Budgens stores, added: "We are incredibly excited to be chosen as a trial site in our 150th year in business. BP asked whether we would be interested. I'm proud of it, it's a good thing for our business."
An M&S spokeswoman suggested the franchise model could be a route to further expansion. She described the move to use a BP franchise as a "possible extension of the partnership in the future".
BP and M&S started the initial trial of M&S Simply Food at BP Connect sites in October 2005. There are currently 113 M&S Simply Food stores in wholly owned BP sites alongside the BP Connect and Wild Bean Café offers.
However, the companies recently admitted that the roll-out of co-branded stores had been scaled back. An initial target of 200 stores by the end of next year has been reduced to 150. BP's UK convenience director Karen Hubbard said the offer did not work in all locations.