http://www.getamap.ordnancesurveyleisure.co.uk/
http://www.nationaltrail.co.uk/
I'm assuming that you were inspired by the movie "The Way" with Martin Sheen to walk the Camino de Santiago.
I was also. But some subsequent googling suggested that, unlike as was portrayed in the movie, a lot of the walk is actually along the side of quite busy roads rather than along idyllic country pathways.
If you have already researched and accepted this aspect of the walk, please excuse me. But it's always good to be fully informed.

Thanks go2.... hope it is useful. You're right though, inspite of TT's problems, it is still a valuable resource.

check out the long distance walking paths/national trails in UK, for example Thames path!

I dont wish to belabour the Thames Path option but it is the only reasonable route from London and its marked well all the way to its source close to the Cotswolds and you cant get lost. It is even signposted from Tower Bridge.
talking to some of my rambling friends, many walkers "cut the corner" with Reading and head thru the Chikterns fron Hambleden ( alledgedly the most used village in England as a film set), just East of Henley and head up thru the valleys thru the beechwoods to Watlington or Walloingfordothers aim for Goring.
But get yourself a decent guidebook and you'll appreciate many of the side trips to windsor, Eton etc.
Whatever yoiu choose to do, I hope the weather is kind to you and you really enjoy your trip.
Graham
Within London Try Walkit which gives you options of quieter routes etc when trying to get between two places in London.
You could also try Map My Run - or indeed Map my walk which I've just found which is good once you have an idea of of a walk to measure the distance.
I'm assuming that you were inspired by the movie "The Way" with Martin Sheen to walk the Camino de Santiago.
No Chris, I haven't seen the film - nor read Shirley MacLaine's book, though most people assume one or the other. The Camino has been on my mind for the past 20 years, but I never thought I'd be able to do it. Now I've suddenly got myself fit it's become a reality.
I'd intended to walk the Camino Frances but, after staying in the hostel in Seville from which many people leave, I've decided to do that one. It's longer @ 1000 km, but flatter. It's also much less crowded but busy enough that there are refugios at convenient stages along the way.
I actually walked half of the first stage with a woman who was also staying at the hostel, both to keep her company and to see how well I could do it. Fan-blooomin'-tastic! I was sorry to have to return to the hostel,but wasn't set up to do it this year.
Alas, Rory - I never was in the scouts and I'm quite useless with a compass. :>(
Coco / Graham - agreed. And thanks for the additional tips.
Lizzie - thanks for the websites. I'll look at them when I sign out of here.

One possible route to consider is Fen Rivers Way, 50 miles / 80km between Cambridge and Kings Lynn, both of which are on a main railway line linking with London Kings Cross. The route passes through Ely, Littleport, Downham Market, all of which have accommodation and railway stations.
see http://www.ldwa.org.uk/ldp/members/show_path.php?path_name=Fen<i>Rivers</i>Way