This depends on your definition of "teenage". Most studies do not appear to include "older" teens (i.e. Beyond the age of 18) as these are seen as adults.
A quick search on the net (thanks Google) suggests that the rate of conception for under 18s is 42 per 1000 over the UK as a whole, or 4%, broadly-speaking. These are probably not definitive figures (although the government seems to use them).
The Family Planning Association website contains a wealth of statistics.
