Misfiring problem.

If i only use the A roads its perfectly fine, but if i get on the motorway for anything longer than 30 minutes, as soon as i exit the motorway and drop the revs down, the engine starts to cough and splutter and eventually dies.
If i leave it for 10 minutes or so switched off, i can start it again and usually makes a massive backfire.

have no idea what could be causing this

I had a similar issue with my 01 a few weeks back. Nice dry (albeit cold) day, hooning along the motorway when the front cylinder cut out completely. Fortunately I was covering the clutch and stopped a spin out. Got to the hard shoulder just as the engine cut out completely.

left for 10 mins then restarted with a massive backfire and ran rough for about a min, idled along the hard shoulder up to motorway speed without any further trouble then continued home. Not the most comfortable expericence.

I had a few issues with this. Occasional cut outs after long stints with a neutral throttle. Only had this hiccup once every two weeks so it wasn't enough to spur me to action.

I Also had problems with the front cylinder cutting out in the rain. (that old chestnut) I checked all the usual stuff with no luck in till i twisted the HT lead where it exits the Ignition coil and a load of water came flooding out!

I quickly replaced the ignition coil which solved the running in the rain problem completely. However a year on and i haven't experienced the Cutouts since either.
I'm still not sure whether it was a direct fix by changing the ignition coil or whether i just nudged something with my elbow but a new ignition coil is a relatively inexpensive item and is fairly easy to change. maybe that's worth a shot?