The car has 82,000 miles on the clock and yes, all 8 spark plugs have been replaced.
The Honda dealer has replaced the Crank Position sensor again and the car has been driving OK for the last 2 days. I'll wait to see if this is a permanent fix, but they did say that a re-learn procedure needs to be done after replacing such a sensor - I can only think that the local garage that replaced the sensor originally didn't have the engine management software to undertake this procedure properly.
I was wondering what my rights were with regard to having to pay for this second sensor as I paid over £400 getting the plugs and coils replaced on the basis of what looks like an incorrect diagnosis from the Honda technician.
Thanks for everybody's replies.