I have a valid residency in Italy (Permesso di Soggiorno), but it is in paper format.
In this page: https://www.gov.uk/check-uk-visa I see a statement in exemptions such as: a common format residence permit issued by an European Economic Area (EEA) country or Switzerland
Although I can travel within the Schengen area with it, I don't know if it is "a common format" and therefore valid for transiting UK.
I am a Turkish citizen and I will not leave the airport area during the transit it
The paper looks like this: