Originally Posted by
Lost-in-Space
On the return assistance will help you through immigration (you won't really be able to use the automatic passport gates) and security. Until last year the assistance person could take you to the head of the security queue, but they stopped that and now you must queue with everyone else - "to make the process more efficient". I told them (strongly!) in person and by email what I thought of that, to which I got a big fat zero of a reply.
I was on a mobility transport vehicle recently at LHR, we went through a separate gate at passport control very quickly.