The first thing i am listing on this page is the web address of the Register of Charities. This is very useful since it means that instead of simply seeing a charity number and assuming that the charity is therefore legit, with a few clicks you can check that the number is indeed registered to that charity. Here is the page: http://www.charitycommission.gov.uk/registeredcharities/first.asp
The main Charity Commission site is at: http://www.charitycommission.gov.uk/
This is a website for a campaign against modern slavery: http://www.notforsalecampaign.org