Police Certificates from the UK and Canada... I'm originally from Brazil but had been living in the UK for about 5 months (for that being so close to 6 months I imagine that the officer decided to check on if I had done something wrong while there - for the certificate from Canada I think they are doing that because they get your fingerprints in the process (something I've never provided)... A friend of mine also had to provide a police certificate from Canada, something he also never had provided until then).what additoinal documents they request from you.