As (a Dutch) participant of this event I am looking forward to this trip and trying to get an idea of the route in terms of climbs, scenery and also safety.
Pictures of the sign in Lands End to John O Croats indicate 873 miles which is 1405 km.
The route therefore must be close to I presume the shortest route? leaving little room for alternative routes for busy roads?
Coming from the Netherlands, I am not very comfortable with riding close to the borders of busy roads while large lorries are passing closely by with relative high speeds (especially at night in the rain) .
Having limited bicycling experience abroad (only PBP 2019) and thus non in England and Scotland, I am a little worried how many roads like this there will be, how safe I will be and also what I can do more than the usual (sufficient lighting, reflective tape on wheels and wearing a reflective safety vest) to decrease risks apart form staying home .
Google maps gives 812 miles by walking or 836 driving, so the 1400+ km is not all that close to the shortest possible route. I would not expect to spend much time on busy main roads
"climbs, scenery"? The profile on the RwGPS route I've drafted (link in my post above) should give you an insight into the 'scenery' (climbs). The number of steep climbs (steeper than 1:10 - do you remember the steep pull up from Longny les Villages (PBP @ 99km)?) is close to nil (Helmsdale @1335km steepest?), so not dissimilar to PBP - similar climb per 100km. As @Ww says, I'm sure the route will be designed to minimise time on main roads [Edit: south of the Clyde] - to a very small percentage. No time on the A30 once it's dualled (at Hayle); bit busy into/through Taunton and Bridgwater; brief moments on the A49, and I've commented on the A6, A82 and A9 below.
Andy's route seems to skirt the southern side of Bodmin Moor - with Minions a 'high'light; crosses Dartmoor (national park) - the climb up from Tavistock is about 370m in 10km with two efforts of one km @ 1:11; crosses the Severn Bridge and up the Wye valley (Forest of Dean and past Tintern Abbey); heads up the Welsh Marches past War of the Roses castles etc, gets an unavoidable urban fix from the Mersey to the Ribble; then enjoys the A6 (with variations into Kendal possibly) - that road takes only local traffic as the M6 takes the heavy stuff - over Demmings Moss (at 426m) to Carlisle. The climb up from Kendal is close to 400m in 16km.
Then it's into Scotland and the 'old main road' to Glasgow (again the M74 takes all the traffic); bypass Glasgow via Paisley to the Erskine Bridge across the Clyde, wiggle up to Loch Lomond, take the low road (A82 - some don't like it) into the Highlands till it gets higher, across Rannoch Moor, down Glen Coe - can't get much higher scenic quotient than that (depends on metric), to Fort William. Head up the Great Glen (stretches of canal towpath with excellent surface available), past the Commando Memorial (with the top of Ben Nevis in view if you're lucky), along the side of Loch Ness ~~~, to Inverness and the A9 up the coast to JoG.
1400km is a very reasonable distance to plan an end-to-end to, minimising time on A roads till Preston, and from Carlisle to Glasgow.
The A6 from Preston to Carlisle is fine (see above). After the Clyde the roads in Scotland are what they are. But this route avoids the 'fast' A9 from Perth to Inverness. And then from the Kessock Bridge onwards the A9 is OK, and there are sections which can be avoided (eg Alness to Tain) with minimal extra distance on parallel decent minor roads. For the last 160km (from Alness) the imperative to keep the route 'short' unfortunately means the rider misses out on solitude on offer on the road up Dornoch Firth and the Kyle of Sutherland to Lairg, past the (LEJOG iconic) Crask Inn, Strathnaver to Bettyhill and the north coast of Scotland - that much more attractive option is 40km longer.