Since I haven't heard back, I am going to revert this for the time being. Note that the limited access nature of the road is already reflected in expressway=yes, which is independent of the classification. I don't think that the road is as important as the other motorways or trunks in the area, which is why I think primary is appropriate.

Also note this section from the national 2021 classification guidelines: "The Trunk classification generally should not be applied to highways that are parallel to motorways, especially highways within a short distance (less than 5 miles) from the motorway."