Without getting up from my chair to have a look, I have a feeling that all UK issued licences state PIC or PIC U/S for the type rating you have. Therefore the upgrade to Captain is purely a company thing. I don't think your licence changes. I don't think all companies ask for logbooks, and anyway, these could easily be faked.
And I guess Sri Lankan didn't ask for a reference from the previous airline, or didn't ask the question?