I get the 90 days out of 180 for most of western Europe. I was on a site that said tourists could stay up to 6 months in the UK. Is it possible to spend 90 days on the continet followed by 90 in the UK?
Yes, because the UK is not part of the Schengen zone.
What Tom said, 90 days out of a 180 day period in Schengen, UK days don't count toward that because they're not Schengen. It's always good to have some documentation of your days outside of Schengen in case you're asked (hotel receipts are perfect). Remember, the 90 day limit is only to travel Visa free. It's been awhile since I had to get a Visa but the standard tourist Visa, as I recall, gives you 180 days.
You should check the Department of State website for the latest information. They have the most recent and accurate information.