Mrs R - there are rules about 'stop and search' that it doesn't sound like the police followed in your case. They must provide you with certain information and paperwork about why they have stopped you etc, and according to Liberty they must have reasonable suspicion. The recent anti-terror legislation widened their powers of stop and search.

Have a look at the following link from the Met's website;

http://www.met.police.uk/stopandsearch/what_is.htm