Monarch used to do 290 kts as standard in the descent, so there must have been some reason for selecting that speed.
Then they changed it to 290 kts back into the uk (i.e. generally busier airspace) and ECON elsewhere.
Now it's ECON everywhere apart from the london TMA where it is 270 kts. This is not a Monarch choice but has been specified.
If everybody flew ECON, which takes into account the current cost of fuel, we would probably all be flying compatible speeds anyway.
Otherwise you can't complain about someone not flying as fast as you think they should be when no speeds have been specified.
I personally don't care what speed I fly. Faster get's me home quicker, slower uses up all my FTL's for the month and I might get to go to work a little less.
FIS.