We are currently reviewing how to best represent this information, I believe you were part of the conversation last year as how the Parking role etc. could be used. Our understanding is that this has not been adopted as a standard tag.
I think this is an area where more work is required, but for now we are not supporting these facilities as part of the trail relate.
How do you think we should promote this concept as part of the OSM UK community?

Please don't do that. I am working with the National Trust Path and Trails Team osm.wiki/Organised_Editing/Activities/National_Trust_Paths that added this information and it is causing issues. Specifically it cause the GPX files to be useless from https://hiking.waymarkedtrails.org/
The information may be useful to explicitly link facilities to trails but how it is set-up is not useful.

I do normally keep edits to more local areas but 1/2 way through this I was asked a question about Fountains Abbey so jumped a round a little. The edits are to remove car parks, cafe's, toilets from Trail relations, as they cause errors on routing etc. The were captured as part of an organised exercise and I spend about a hour a week removing them as I couldn't find a good way to automate it.