Lumpy petrol vrs

Hi, first post here! I have been looking around here for a while and found some useful information about my problem. I have tried a few fixes but nothing has sorted it yet so any advice would be very welcome.

I have a 2007 vrs petrol estate with 93k and the engine has become lumpy and a bit sluggish on normal acceleration when cold. When the revs go above 2500, the engine goes smooth. It appears to be more lumpy if the engine is having to work harder , i.e. going up a hill. It feels like it is missing every now and again. The problem seems to be getting worse as time goes on ( I first noticed it about a year ago) and it also seems to be worse the colder the ambient air is.

When the engine is at normal temp it is fine although I'm sure performance and fuel economy has dropped off a bit. I've had the car since 73k(2years ago) and it had belonged to my father-in-law from new so I know it's history is all ok

What I have done to try and fix it:

Treated the petrol with a tin of bg44k

Replaced the ecu temp sensor (the one on the side of the engine)

Took it in to our local garage to plug it in to see if there were any fault codes. Nothing showed up other than a code which turned out to relate to an intermittent fault on the cruise control ( I have not noticed any malfunction of the cruise)

And today I have just swapped all the coil packs.

None of the above made any difference. Not sure where to go looking now?