I am sure you are already in contact with VSO about their youth programmes, which especially focus on the impact of exchanges etc on return volunteers to UK in the context of promoting 'global citizenship' and deeper understanding of and involvement in both development education and volunteering in UK. They also work with their long term return volunteers and have a lot of information about them I think.
A good person to guide you through the VSO information could be [log in to unmask], if you are not already on top of their work. The British Council work with VSO now running a major youth programme to promote inter-cultural understanding and finding ways to assess how/when and whether that happens would be interesting and challenging for any study of returned volunteers.
There have been some conferences in the past year on the issue but I do not have the information to hand.
DFID will be funding Christian Aid and Islamic relief to run a very large short term volunteer programme for young people from UK again with a view to promoting inter-faith understanding and development awareness. tracking that in future will be important but I am not sure how the agencies are defining development awareness or better inter-cultural/faith understanding at this stage.
I expect this is all known to you but you gave little idea of what you have already done and who you have contacted so I have started with the obvious.
Tina Wallace