Check the best sites for finding statistics and data from our Statistics guide
There is no comprehensive directory of these organisations, but Wikipedia provides a list of of UK think tanks which links you to their websites.
Check the Official Publications' page of the Law subject guide for a list of relevant sites
You should always evaluate the information you use but especially so if it is available freely on the internet.
The SIFT (four moves) method devised by Mike Caulfield suggests 4 things to do when looking at a source to help you evaluate it.