If you mean part-time jobs for teenagers still at school, in the 1990s it was about 40%, but in the last few years it has dropped dramatically and is now only about 20% (about 250,000 in total). The reasons for this are partly to do with the recession - the typical part time jobs for school students are in retail, or bar work for older ones - and the sectors which employ them are in decline. Work experience schemes have also been cut, and these were a good way for school-age people to find work. Another reason is that more young people are putting their studies first and not opting to work part-time unless they really have to.
Among teenagers with part-time jobs, a paper round is still the most common, largely because you can start from the age of 13 which some jobs don't allow. Out of the total number of teenagers with jobs, the percentage doing a paper round is generally about 25 to 30% depending on the area.