My route would be to go up to Barnet, through Hadley Wood and then Potters Bar, then through Essendon to Hertford. Then go through Crouchfields to Wadesmill (just north of Ware), and head on up to Puckeridge. Then it's B1368 time all the way up to Hauxton. Go through Cambridge, and head north on the Histon road, passing through Cottenham up to Wilburton on Twenty Pence Road. At Wilburton go down Station Road towards Witchford. If nothing else that route means you can truthfully claim to have ridden on Grunty Fen Road. At Witchford turn right towards the Lancaster Way roundabout and then it's a quick A142 to Ely, or the cyclepath on the LHS of the A142 if you're not feeling brave.
I live in Ely, so it's a route I've done quite a few times, albeit usually in the opposite direction.
... I love that bike/toy shop there, do you use them?
Ely City Cycles? Yes, occasionally. Mostly for bar tape and recovery drink powder. Trouble is, I work very close to Condor Cycles, and so that's usually more convenient. If very, very dangerous given all the nice kit they have in there.
My route would be to go up to Barnet, through Hadley Wood and then Potters Bar, then through Essendon to Hertford. Then go through Crouchfields to Wadesmill (just north of Ware), and head on up to Puckeridge. Then it's B1368 time all the way up to Hauxton. Go through Cambridge, and head north on the Histon road, passing through Cottenham up to Wilburton on Twenty Pence Road. At Wilburton go down Station Road towards Witchford. If nothing else that route means you can truthfully claim to have ridden on Grunty Fen Road. At Witchford turn right towards the Lancaster Way roundabout and then it's a quick A142 to Ely, or the cyclepath on the LHS of the A142 if you're not feeling brave.
I live in Ely, so it's a route I've done quite a few times, albeit usually in the opposite direction.