SenecaGirl, looking at the locations of some of the posters I would reckon that they are looking at using BGS for JAA licences from the premise that they already hold an ICAO PPL.
Bristol only do distance learning for modular training so a PPL is a minimum requirement in order to enrol.
There could be many reasons why someone would want to convert from, say, FAA to JAA but mostly it's to do with which countries you have the right to work in! Some people may go to the States to do FAA licences and then convert to their own county's licence as they perceive i tot to be cheaper; others may need to convert due to personal circumstances taking them to another country.
Cheers
Whirls