Some good options here, in various parts of the UK, promoted by organisers of the Dirty Reiver: “Dirty Reiver Regional - September 2020” https://www.komoot.com/collection/1011381/-dirty-reiver-regional-september-2020
And some more here : https://www.redbull.com/gb-en/best-gravel-riding-routes-uk
I thought this was just a US site, but I just did a search for London and it brought up lots of gravel options…dunno how accurate the data is, but I have used this a fair amount for stuff in the US.
ETA - ooops…I missed @KatuskaMTB post above. he already posted it. My bad!!
Wow! How have I never seen this site? Thanks for sharing!
You don’t need to limit yourself to gravel roads. I’ve been riding my gravel bike on trails that are generally considered mountain biking trails and it’s quite fun.
As said above it all depends on where you are in the UK. In the north east of England, wales or especially Scotland you are almost spoiled for choice. In the south of Scotland, where I live, there are loads of wind farms with pretty decent Gravel tracks that are easy to access. Some of the best off-road rides I have done are the linking of these wind farms with backroads and could easily get a 100km ride with 60%+ gravel and boat-load of climbing. Best way to find them IMO is to go on Strava heat-maps and cross reference it with a road map/ OS map to find which of the thousands of marked tracks is actually usable.