cristian,
by probability jane meant that marsh warbler has just a couple of breeding pairs in england, between 11 and 34 bp according to EBCC (in 2000), while reed warbler is common. don't know if we can trust in the estimation of a half million breeding pairs of marsh warbler in romania though. but then, why not.
btw. to me the acrocephalus you posted recently looked like a marsh warbler also. it had a short and blunt bill, dull colours.
this bird is not young, but an adult near its nest.