No, there are usually no emergency exit rows in economy flex, at least not onboard MD80 which is the aircraft mostly used for ARN-LHR flights (occasionally they use B737-600 as well).
The exact number of economy flex rows is hard to predict as it depends on demand, but usually it is one or two rows behind C (like row 4-6), or when demand is very high it can stretch to row 13-15.
But still no emergency exit...

I have yet to see a cramped economy flex cabin though, so I wouldn't worry too much if I were you...