Hi. I can acknowledge the lack of official expressway classification. However the tag is appropriate here according to the OSM wiki ( https://wiki.openstreetmap.org/wiki/Key:expressway ).

I added the tag here specifically as the road meets the criteria of it being a dual carriageway, having controlled/limited access i.e. sliproads, and having a relatively high travel speed.

I am adding the tag more widely as the classification of roads in the UK (e.g. highway=trunk) doesn't reflect the design and features of a road, but instead the strategic classification choices by government entities. This is unlike the tagging in other countries which tag based on their opinions. For example in France, there are breaks in otherwise highway=trunk routes just because the road is a single carriageway for a short stretch.

In short, this isn't a tag introduced to reflect a formal classification, but to reflect the high-speed design features of a road, where the highway=* key covers the formal classification already.

Cheers,
Sam.