Mondeo 1.8 - lack of engine power, now worse

1993 Mondeo 1.8 petrol RHD
I'll come clean to start with... a while ago I ran out of fuel and have been told that this can play havoc with the fuel system as it can lead to any
gunk in the tank being sucked into it.
Now then... For the last few weeks I (my car!) have began losing power. I could accelerate to start with but would soon reach a sudden - and quite definite - speed limit for certain gears, 1st would barely get me past 10mph, 2nd maybe 30, 3rd barely 50, 4th maybe 60 and 5th 70mph tops. Pressing the accelerator harder would lead to a dull humming noise that initially had me thinking I had lost a plug. Occassionally the engine would judder as though it wasn't getting fuel.
Whilst out earlier and in a bad mood I was sitting at 60mph in 4th, foot absolutely nailed to the floor, when something gave up. I now get a hissing noise like a leaking air line from the lower left of the engine when I press the accelerator (I'm in the car here - lower right if looking into the engine itself), higher revs give a louder hissing noise.
All the problems I have happen while on the move and not when the car is stationary in neutral (when it seems to rev up just fine). There is no backfiring.
I have several possible causes given by a Haynes manual -
i) timing belt issue - NO - no backfiring ii) fuel filter choked - POSSIBLE - full of sh1t from tank after running out of fuel iii) ignition timing - NO - again no backfirig iv) faulty fuel pump - NO - that's behind me v) uneven / low cylinder pressure - ? vi) worn, faulty or incorrectly spaced spark plugs - MAYBE - but doesn't account for hissing vii) vacuum leak at the inlet manifold or associated hoses - POSSIBLE - explains hiss, but should cause backfiring (apparently) vii) blocked injector - POSSIBLE - but does not explain hissing sound and should also cause backfiring ix) brakes binding - NO - they aren't x) clutch slipping - NO - it is (a bit) but does not explain my problem.
I think I may have several related problems, possibly starting with a choked fuel filter which has in turn led to other problems deeper in the engine...
Any suggestions?
Martin If you want then start to laugh, If you must then start to cry, Be yourself, don't hide, Just believe in destiny.
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Paul M Brierley opined in

does ... or I should say.. DID your car have a catalytic converter on it?
Unsure when the UK started requiring them
Perhaps that gunk story worked in the past.. and you can tell once you change your fuel filter, but your CURRENT problem sounds like a plugged cat, no not a dead feline!.. (or does it?)
Where did you get the petrol when you ran out?
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Yes it does have a cat and afaik the petrol that was put in when I ran out was bog-standard unleaded...
I'll check out the cat, cheers.
Martin

change
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