Part 1 deals with Covert Photography
Part 2 deals with Stop and Search
both are very illuminating and go a long way to dispel some of the myths surrounding the law in the UK. I'm looking forward to reading a few more in the series.
Was it legal for me to take this picture - read the articles to find out.
On the same subject there is a pdf guide to UK photographers rights available here though it is now three years old so some of the information may be out of date.