This was until 2005 all a single property with an address on West Street, the main west-east road you can see.
It was then converted into flats and given the name “Isinglass Mews”.
The address is formatted as:
Flat X, Isinglass Mews,
West Street, Coggeshall,
Colchester,
Essex
So it seems historically Isinglass Mews should be treated as a place, but many might imagine that it is a cul-de-sac.
I would like to add it to the map to make it easier to find, and I think if I add a small stub-road with the name Isinglass Mews at the beginning of the car park entrance, this would serve the purpose. But at the same time I don’t want to contribute to a “corruption” of the OpenStreetMap by adding roads that aren’t technically roads.
Difficult question… My first thought was to use addr:housename but I don’t know if and how OSM-Applications will evealuate this key for a search or routing. As the wiki mentions that it is common (that houses without housenumber but with a name exists) in the UK this realy might be a specific question for the UK-Forum. Note that there are also Mailinglists where you can post your question(s).
The UK section of this forum is not very active. The Talk-GB mailing list is a bit busier, so maybe better to ask there.
As for the question, this can be a fairly common thing in the UK, and there can be a few different ways of tagging/mapping this. I think it depends on how the address is used, and how it is signposted.
If it is just a single building (with multiple flats within it), then I would probably tag the building with addr:housename. eg addr:housename=Isinglass Mews, addr:street=West Street
Whereas if its several separate buildings, all with the same name, then I might say it is a streetname. Especially if there are signs which look like streetsigns. For mapping a streetname, you can draw the driveway, or service road into the car park as you suggest, and tag that with the name. Or you could say it is an alternative name for part of the main road. So split that road, and tag part of it with alt_name=Isinglass Mews (or name:left / name:right if the name only applies to one side of the road)
Or both of these, if there are entrances to the building from the main road and the car park. Plus tag the building as addr:street=Isinglass Mews