I'm getting a misfire code for cylinders 1 and 3. Yesterday the emissions symbol was flashing on the dash and the car was shuddering badly in 5th gear. 

 

I suspect its the ignition coils. 

 

Are these straightforward to replace, just pop them off, disconnect and fit new coil?

Yes, though they can be a pain to get out. Some use wire in an X shape underneath the head of the coil, I used cable ties to similar effect which worked quite well. 

Should have said - try switching them around and see if the fault follows the coil moves first!

It could be coils. They do fail. As @-mike- says swap positions around and see if misfire cylinders move.

 

The cable tie trick works quite well or you can get a coil puller tool but then tend to vary with different designer coil packs. 

 

A little dialetric grease on the coil pack seals can help subsequent removal. 

 

Also, the other obvious go to is plugs. How old are they? 

4 hours ago, TheClient said:

It could be coils. They do fail. As @-mike- says swap positions around and see if misfire cylinders move.

 

The cable tie trick works quite well or you can get a coil puller tool but then tend to vary with different designer coil packs. 

 

A little dialetric grease on the coil pack seals can help subsequent removal. 

 

Also, the other obvious go to is plugs. How old are they? 

I had the plugs changed at the garage about a week ago.