Renault clio misfire - already changed coil pack and plugs

Hi,

Around a year ago, my Renault Clio, 1.2 16v 2005 begun to miss fire. I had AA cover so called them out and plugged the car in. Error code said the car was misfiring on cylinder 1 so I got myself a new coil pack. Problem went away for around 2 weeks until it started raining and the car misfired intermittently. Easily solved at the time, just rev it a bit and it carries on.
Problem persisted but I carried on driving just getting used to avoiding the misfire.
Around a month ago, car begun to start spluttering whilst idling and would misfire.
Today I decided to get another coil pack to see whether that would solve it again, changed the plugs too. Bloody problem still persists even when it is not wet., happens at any revs, any speed, any temperature.
I am unable to plug it in to a diagnostics computer so will be relying on your suggestions and advice.
Main reason i am asking is because I am looking to sell the car but I'd like to fix it before I sell it because I dont want to pass any problems on to a new owner.

Any help would be greatly appreciated.

Thanks in advance,
Jasper