Hi Dancing
At the moment I am just considering the possibility of doing a PhD.
If I went ahead, my situation would be very similar to yours, so this topic has real resonance with me.
First I would contact the student advisory services at your university - can they shed any light?
Then compare what they say to what the Citizens Advice Bureau says. CAB advice is not always accurate. They might not have encountered such a specialised situation before. So you need to have a spread of advice if possible.
It's probably worth while checking out the general advice available from the Tax credit web sites as well.
Are you a member of a trade union - can they do any checking for you?
Best luck
Angelette8-)