UK tax return policy

Hi there,

I am writing to ask if some of you could help about how the tax return works in the UK. I have been a postdoc in the US and Canada, and in both places I had my taxes back, what was a considerable amount of money out of my grant. Here, with a MC, the taxes raised to around 40%... Will we have this amount back? how and when should be presented the tax return forms? 

Thank you.

A.