I did a similar trip in 1980. Turned south from Turkey because the Iranian revolution had just taken place. I went through Syria, Jordan, Saudia Arabia, Kuwait, back into Saudi because no boats down the Gulf, Qatar, UAE where I finally got a local boat to Karachi. Probably not as interesting as your intended route. I found that no matter how difficult people told me it was to get a visa for the next country there was usually a way to get in. Saudia would only issue a transit visa, there was no such thing as a tourist visa. So if even you can't get a visa in the UK, you may find you can get one in Turkey.
Edward Genochio should have plenty of info on the Russian route:
http://www.2wheels.org.uk/
Yes you are dead right about camping in SE Asia ...send your camping gear home. Hotels are cheap and I can't remember seeing a camping site.
Remember your life may change on such a trip so don't bank of returning to old blighty!