I'm almost certain that someone has probably done this faster, but I've been unable to find a fastest unsupported time so I guess that "fastest known" applies here. Either way, here's a pretty beatable time for anyone who's actually a serious runner to go and take.
I set off with the plan of this being unsupported, stashing water in bushes on route strategically before parking up in Winchcombe, food for the day would be a mix of peanut butter (crunchy, obviously) and/or raspberry jam sandwiches and banana bread and I carried enough to eat for 12 hours from the get go rather than stash food with my water. I was carrying a 3L bladder in my Osprey Duro 15, probably overkill but better to be safe than sorry and I certainly don't think I'd have been able to carry everything in my ADV Skin 5. If things went haywire I allowed myself permission for this to be a self supported run and use the pubs/shops on route to fuel but thankfully I didn't need to resort to that.
I parked in Back Lane car park which is a bargain at £1 for the day and made my way to the High Street/Abbey Terrace to start. The GPX file from LDWA has you start on the Western Loop heading North out of Winchcombe towards Dumbleton and then tackling the Eastern loop afterwards heading towards Gutting Wood and Snowshill Manor House, I'm presuming this is the standard way of doing it as this is how it is laid out in the Winchcombe Way guide book so that's the route I decided to follow.
I started at the War Memorial and headed off, you're pretty much straight into a climb out of Winchcombe from here. At the top I took the wrong path but doubled back. Also a note on the path coming through the fields after Naunton Lane Farm; this time of year it's become severely overgrown to the point I'd consider it impassable, I opted to skirt around the copse of trees rather than get ripped to shreds by briars and brambles.
Signage and path visibility for the most part on the route is good but there are areas where it becomes quite sparse. For example the path running through Dumbleton Estate, there is no sign to say you are on track when you enter nor on the path you are meant to follow until you exit the forest, which was a relief to see but it was only because I had the map on my watch that I knew I was on the right path. Same as the path through the fields at mile ~12-13, the path practically disappears, trying to stick to the line was impossible with the overgrowth of thistles, add to that many resting cows and I decided to take the most reasonable line I could in this situation.
Possibly the most pleasant part of the entire route is the path coming across Cleeve Hill golf course, very atmospheric with the morning low cloud, probably made all the better after quite a slog of a hill beforehand.
Before getting back to Winchcombe I also got to see the highly impressive Belas Knap Long Barrow, made all the better for having 2 biwing planes pass overhead as I reached it. I did consider going inside but decided to stay on track.
After getting back to Winchcombe I headed to my water stash that I placed just off path in the field behind Castle Street, I refilled my water bladder and took my first proper rest, there seemed to be a running event going on that day so I offered the last bits of my water to some runners who kindly offered to take the empty bottles to the bin for me. I set off again briefly taking the wrong path in this field but soon course corrected when I noticed (another field that seemingly didn't have the best signage.)
About 5 or so hours and a few miles into the Eastern Loop in I started to suffer with GI issues, these disappated at first but returned with a vengeance later in the day which I found very sapping of my energy, it practically killed my appetite and eventually inevitably slowed my pace to a walk, coupled that with legs that were seizing up and I couldn't do much more than a fast stumble downhill and get my head down and walk the rest.
The rest of this Eastern Loop soon became a "just get it finished" type of day, despite passing through some beautiful villages my stomach issues and low energy meant I couldn't really take any enjoyment of it, although Snowshill is undoubtedly beautiful. By the time I was passing Hailes Abbey I was all but spent and my desired finish time long passed. But nonetheless I made it back to Winchcombe and gave the war memorial a tap and the day was done.
Not the most impressive time for a route of this distance, I'm certain a lot of people could very easily do better and I look forward to the day someone does. But I'm glad to have gone and done it nonetheless.