There's no concrete answer here on how to optimize this!
However, what I can recommend is picking the 1-2 offices where you legitimatelly have a connection and apply to those.
If you have never worked in London, never been there, and don't have rights to the EU, I would focus on Middle East and Home country. Same goes for Middle East if the situation is the reverse.
You need to 1) Have evidence on your resume that you know/understand/can work in the target office country and (ideally) 2) have networked with people in that office. Otherwise you're just another name on the table!
Think about it, if you were a recruite rin London and you looked at your resume (amongst all the other thousands), would you interview you?