Just read this from a former diplomat
Charles Crawford is a former diplomat, and he has just blogged his own views on some of the questions you have been asking.
See http://www.charlescrawford.biz/blog/diplomatic-bags-assange-
Having gone through a full cheery diplomatic career without having read the Vienna Convention, I thought that I would see if J Assange might be popp'd in an Ecuadoran Diplomatic Bag and removed from the UK that way.
In other words, can he be 'smuggled' out in broad sight or secretly, the Ecuadoreans claiming that their diplomatic bags are immune from search?
Sorry. No.
Here is some handy guidance from (of all people) HM Customs and Revenue sharing with us a Note from FCO Protocol Directorate:
Missions are further reminded that in deciding whether particular articles may be carried in a diplomatic bag they are required to observe the requirements not only of Article 27.4 (“only diplomatic documents or articles intended for official use”) but also of Article 41.1 (“laws and regulations of the receiving state”).
It is particularly stressed in this context that the regulations governing the import and possession of firearms in the UK are among those which must be observed, regardless of any claim that any firearms may be intended for official use.
In other words, if a man-shaped diplomatic bag is seen emerging from the Ecuadorean Embassy and we prod it with a pitchfork to confirm that it contains only diplomatic items, a squeak of 'Ouch!" would give us all the legal options we need to ask the Ecuador Embassy politely to undo it and show us what or who is therein.
QED.