You can also look on
http://findaproperty.com or
http://rightmove.co.uk. But like geeta said, you'll be hard pressed to get a truly accurate idea until you are prepared to move. Estate agents probably won't talk to you until you're in the country, especially if you settle in London.
My advice would be to come over and visit different areas, decide where you prefer and why. You may like London, you may hate it. You may like Leeds or York or Manchester or Cumbria or the Outer Hebrides. You won't know until you spend time visiting locations. And with 5 years of lead time, you have eons to figure it out.
More than anything though, I'd be doing everything you can to find out about changing visa situations because what things look like now will be vastly different in 5 years, especially with a coalition government and promises of changing immigration laws. Without a way into the country, where you live is moot.