someone else trying to panic you, playing the word game! ok i forgot to say stop driving and sort it immediately, but then i like to think you had worked that out
(slapped wrists for me, happy kempie??)
the fuel filter is really just an advisory thing , i know of 3 vehicles that misfuelled (one the middle of last year ) all advised to change filters, none did , they are all still happily driving around one of them a 307 i will be doing during a routine service next month.
In Peugeots of a similar age & size its under the bonnet in a plastic housing in the fuel line to the pump i would assume it would be in the same place, if so its easy to replace but any doubt get a local mechanic to do it 5min job tops. Sometimes it takes a minute to fire up due to the air that gets in thats when panic sets in , but this is normal.Also the management light may come on but this should go out once the fuel pressure is up to spec.
By the way just going back to my original statement, i have worked in the motortrade (all main dealers )for over 30 years as yet i have never know an engine or injector pump or anything mechanical related to the fuel system fail due to misfueling....im not saying they dont but i have never come across it .