Its working @leandrojmp - thanks very much. to change it in beats wasn't trivial (not with my knowledge anyway) so i changed postgres to log in UTC and boom - all works as expected.. I am surprised that with me simply using the default postgres module in Filebeat then this isn't more common issue - i found this that seems to be the same issue but the solution doesn't work for me.
Thanks again for pointing in me in the right direction..