London to Glastonbury route

A friend and I are cycling to the festival this year. He did it once before but, relying entirely on Michelin , his route was high-traffic and very hilly (he's got no cartilage left in his knees so can't stand on the pedals. So I've come up with what looks like a flattish and not too A-road oriented route, but not knowing much of it myself I'm sure there will be sections where someone with a bit of local knowledge can photoshop out some of the busier roads. Any help gratefully received http://www.mapmyride.com/routes/view/187191722
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The route for me always starts at Staines railway st as I can't be arsed to cycle across London and goes through.
Windsor great park, Winkfield Row, Binfield, Wokingham, Barkham, Spencers Wood, Grazeley Green, Ashford Hill, Enborne, Kintbury, Hungerford, Belmore Copse, Burbage, Pewsey, Upavon, Urchfont, Westbury, Frome, Chantry, Shepton Mallet, Wells and on to Glastonbury.
It's a pleasant route avoiding A roads as much as is practicle whilst still covering ground with no real stings in the tail either.
I hope this is of some use to you
JS