OO-AOG is right I think: both airlines operate this route, VEX with 737, DAT with Avro RJ.
Their early afternoon flights were these:
16/11 14:35 London LHR TV 5823
16/11 14:55 London LHR SN 3823
20 minutes difference in departure time and... almost the same flight n°. Could this be a remainder of the SN/VEX agreement ?
I would rather be flying...