A while ago I had to cover a Sarkosy visit to London. The Special Branch Liason officer 'overseeing' me had some great stories regarding similar 'Presidential visits' including a full on fist fight between Special Branch and a Venezuelan Prot team looking after Chavez who had sneaked in firearms via diplomatic luggage. This was prompted by me asking about foreigners carrying firearms on British soil.
As has been mentioned here many times 'officially' none do but in reality only the Secret Service and Shin Bet are allowed to 'carry' - and then only the closest prot members to the principle.
Not that it matters where the French are concerned:
French agents tasked with protecting president Francois Hollande forgot to pack their guns for Rio Earth Summit | Mail Online