They may be trying to determine how quickly the British respond, get some insight into intercept methods, maybe to pick up possible comm frequencies. Either preparing for a wider war in the Med., or at least trying to show Obama that they are ready for one.
I quite agree. This is a bit like some of the probes during the Cold War.
If memory serves, the Syrian Air Force operates the Su-24MK.
This is an of itself should tell us that the Syrians/Russians/Iranians/Hizbollah/Norks all need a lesson taught to them.
They know the British Parliament voted to sit this one out so what is the typical Arab response, probe and give you the finger for chickening out. They love to humiliate those that back down.