Originally Posted by
simons1
To actually answer the OP's question there is no difference in the seat. It is an economy seat, the only difference is the middle seat next to you is empty.
I respectfully disagree. The fact that the middle seat is empty changes the game so much that the seat is, in effect, no longer the same. I personally find the whole CE experience so much better than ET (although my frame of reference is actually UK Domestic) that it might as well be a different seat.
Originally Posted by
simons1
I wouldn't compare to the trains, on most inter city services (and Eurostar and even some commuter) the F seat in trains is different, usually bigger, 2-1 across as opposed to 2-2.
The British Rail Mark 4 carriage is 8' 11" wide (source:
wikipedia 
) and the Airbus 320 cabin width is 12' 2" (source:
wikipedia ), so the 320 offers approximately 36.4% more useable width and an extra 33% of seats across (i.e. from three to four) makes Club Europe on the planes entirely similar to First Class on the trains.