This is my speculation on the route — pure speculation based on the info Tomsk has posted here. It's Gavin & Stacey plus a hilly Welsh loop and a modified retour: https://ridewithgps.com/routes/26526898. I repeat — this is me just joining the dots, nothing more than that. Just over 1040km by my reckoning, but plenty of opportunities to shorten for the brave.
1000km cycling event
starting from Witham(not Billericay), Essex. Controls at Buntingford, St Neots, Towcester, Banbury, Tewkesbury, Chepstow, Pontypridd, Barry, Tonypandy, Llandovery, Neath, Barry, Chepstow, Pershore, Wellesbourne, Towcester, St Neots and Buntingford.
I look forward to be impressed to see a route with these controls coming out at less than 1050km without disproportionate minor road wiggling. My stab is 1050km (starts and finishes in Witham).
Would we be allowed more time if this was designed as a 1100km BRM ride? We'd get a full fourth day's ride in. [Edit: "BRM (Brevets de Randonneurs Mondiaux) events are run all around the world under the standard set of rules laid down by the ACP (Audax Club Parisien) and the rides are validated and recorded by them. They are at standard distances, with a maximum of 5% over distance, and the maximum time limits for each distance is: 1000km 75h00 ." So 1050km is the maximum distance if the ride is to be a BRM.]