In reply to all:
Thanks for the suggestions all - Exile, I looked on a map at your route and will definitely keep it in mind for a future mission.
In the end I went to the Howgills and Yorkshire Dales. It was wonderful but also hard work. I consider myself moderately cycling and hill fit, I commute 100 kms a week and my ride home involves 260 mtrs of ascent, so I'm not unused to hills, but I had not paid enough attention to the ascent in my planned route!
Day 1 I parked in Sedbergh and went straight up onto the Howgills. Some pushing was needed but not too much (pushing the bike with camping gear and three days food on it wasn't that easy either!). From the highest point (the Calf?) the descent north down Bowderdale Beck is amazing. It's a bridleway so all legal and proper but on the ground its just the single track descent that goes on and on and on. Probably the best descent I've done on a mountain bike. I then went east and picked up the top of the Pennine Bridleway. Immediately you do another huge climb most of the way up Wild Boar Fell. The descent east from shoulder you reach is pretty mental too. Superb fun going down but I thought it must be heart braking for anyone trying to finish the PB (coming from the south), as pushing your bike up it must be so hard. The PB then takes another hard slog on a gravel track up the other side of that Dale, before taking a traverse line along the side of the valley that just goes on for miles. The PB drops down to Garsdale Head, but I carried on traversing on this remarkable bridleway (supposedly called Lady Anne's Road) before the final marvellous plunge into the valley just west of Hawes, where I stopped on a campsite for the night. 55 kms and over 1500 mtrs of climbing!
The next day I was definitely still feeling it so altered my route a little. I didn't go the whole way up the hill above Hawes to get on the start of the roman road - the Cam High Road, but traversed up to it about halfway the along the ridge it drops down. A few kms of fast dead straight but still rocky roman engineering took me to Bainbridge. From there I climbed southwards up on tarmac then tracks onto the high plateau before another huge descent into Langstrothdale. I was going to do another supposedly hard climb and excellent descent over a ridge south in to Littondale but my legs weren't really up for it, so instead went up to Langstrothdale to where you can cross over and drop in Ribblesdale, and down to Horton where I camped the next night. 42 kms but still 800 mtrs of ascent.
Yesterday I whimped out a bit of using the PB north from Horton and instead rode the road to Ribblehead, but then it was a good but tough climb up the side of Whernside, where the bridleway takes you NW above the head of Dentdale - amazing views down the dale to the Lakes and the Howgills. The descent down to Dentdale is also brilliant riding. I had originally planned to slog up the road here and take a track that traverse high above the dale again, but with thoughts of getting home and seeing the family and the tiredness in my legs - well all over actually - I followed lanes along the dale bottom instead. Even still I decided to follow a bridleway for the last bit that took me through a ford across the River Dee which was amusing! And then another tough climb up the north slope of the valley and a few more kms of fantastic single track down right back to Sedbergh where I had left my car.
I've never ridden in the Yorkshire Dales, but it's bloody brilliant I thought. If you enjoy mountain bike and also haven't I can thoroughly recommend it. Just don't underestimate how many climbs there are even if they aren't quite Scottish- or Lakes-sized!