I am familiar with the majority of this route; I walked the middle 3/5 of it today (3 May 2021), from Kington Langley to Corston.
I joined the route on Day's Lane in Kington Langley. I found it impossible to get onto Chimal One by the right turn onto the footpath at Lipgate Farm because the gate was tied shut. However, there was an easy workaround by continuing to walk along Day's Lane, and turning right onto the Byway after about 200 yards, then left onto the Chimal One footpath. (This left turn was not marked by a visible fingerpost or way marker).
The footpath across the planted field was not well marked or visible, but I got to the stream at the bottom. I expected to find a footbridge, but there wasn't one, and there was no finger post or way marker. I eventually found a way across the stream by scrambling down and up the banks and getting any feet wet walking across. Certainly not possible with wheels.

The path from there to South Sea Farm was OK, but I had to duck under electric fence wire a couple of times. The route though Whitelands Farm was a bit more difficult, but I got there in the end. No complaints about 100 yds through cow slurry. It is the countryside after all.

Approaching the new St Modwen Distribution Centre / Eyesore / White Elephant on the B4122 I found that there had been a (presumably legal / authorised) footpath diversion about a quarter of mile before the B4122. (See photo). It took me left to Day's Lane then stopped, leaving me to walk along Day's Lane and onto the grass verge alongside the A350. So then it was a quarter of a mile along a narrow grass verge, dodging empty bottles and Costa cups by a very busy 60mph dual carriageway. Not for the faint hearted or those with wheels. Then around the M4 roundabout to the relative safety of the grass verge alongside the A429 and the right turn to Clanville.
For the historians, 150-250 years ago the road to Clanville was part of the main Bath-Oxford road, aka the Pucklechurch to Christian Malford Turnpike.
The left turn onto the footpath was not marked, but relatively easy to spot, before the white house (see photo). From there it was relatively plain sailing. Except for being confronted by two very loud dogs, off their leads and without any owners in sight, as I approached the Stanton Road. Once across, the bridle path to Rodbourne and then on to Corston was OK, if nondescript. Although I did see 3 deer.
For those who reach Corston and want to save a bit of time, note that there is a safe and usable pavement / footpath / pavement all the way from Corston to Malmesbury alongside the A429.

All told, I can't recommend it to give this more than a 1*.
1. be safe - not really, especially on the A350
2. respect local codes and laws -OK?
3. be accessible to as many people as possible - no
4. be direct - OK
5. be off road - mainly, except for the bit along A350 and around the M4 J17
6.. have resting places to eat or sleep every 5-10km - Yes; note that there is a Truck Stop cafe down the B4122, just after the St Modwen site
7. pass through train and bus stations - Yes
8. be easy to navigate - OK with a map but a remarkable lack of Fingerposts and way markers
9. be enjoyable and beautiful - Not really
10 use established routes (such as the Welsh Coast Path), but not be distracted by them! not really.

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