I will apply for an extension in December and because I would like to make a personal application, I used the following link
http://www.ukba.homeoffice.gov.uk/book-appointment
I was asked "the case ID" in the 3rd screen. According to the explanation given in the page
Your case ID is a unique numeric reference for your application. You can find it on your invitation letter.

http://imageshack.us/photo/my-images/198/caseid.png
Can anyone clarify what this "invitation letter" is for extension of Tier 1?
I have received the HSMP back in 2008 and then delivered it to switch to Tier 1 in 2009. I do not know any invitation letter other than that? What am I missing?
cheers



