OK, travel arrangements: -
If I take my own car (a Fiesta) I can fit in Simon, Joey and Thom as planned.
If I hire a 7 seater Zafira (additional cost but probably more reliable) then I can get another three cubers in and we can spread the cost (whilst having a good laugh on the way).
Jude and Rowan get dibs as they're conveniently located (and good company of course).
It would be so much quicker and easier if Thom and Joey can somehow
make their way to Sheffield rather than be somewhere near the Orkneys

.
For Chris we'd have to drive over to Cambridge, use the A1, M25
which is a detour of 140 miles (about 2.5 hrs) according to Google Maps
Nottingham -> Sheffield -> Cambridge -> Bristol
361 mi – about 6 hours 31 mins
Nottingham -> Sheffield -> Bristol
223 mi – about 4 hours 0 mins
So that's not looking too promising I'm afraid Chris

-- can you get yourself to a better waypoint on the Friday? Looking at
http://www.nationalrail.co.uk/ -- Cambrige to Sheffield and Cambridge to Nottingham.
If not Chris then there's another seat free if we go for the 7 seater.
Vehicles with more capacity are significantly higher priced - the diesel Zafira seems the most reasonable (£90 for the weekend from
http://www.europcar.co.uk/).