2002 406 Rapier Estate engine problem

My 406 Rapier Estate has recently given me trouble. I got an error
message on the display saying "anti pollution fault" this lasts for
around 4 seconds at the same time an orange light in the shape of an
engine appears on the dashboard, this stays on. I have had the car
looked at and an expensive fuel pressure regulator fitted, this
following replacement of the low pressure fuel pump in the top of the
fuel tank. I was told this had broken up and fine pieces had got into
the regulator hence the replacement. I was told the car was fixed and
when I picked it up it seemed much improved. However with half an
hour the "Anti pollution fault" sign reapeared and the car reverted
to limp mode, it won’t rev higher than 3000 revs. If all this is not
bad enough the engine has now started to cut out while I am actually
driving the car, most disconcerting and possitively dangerous while
driving in traffic. Has anyone had similar problems and can anyone
explain what and anti pollution fault actually is. Any help would be
very much appreciated. thanks, Pete