About a week later we've recieved both copies of the bill, and Matthew has written 'jda paid by phone/switch 7/3/03' on one of them. All seems fine.
Yesterday, we get a letter (sent to `Jm Messrs Woodford'!) from a debt collections agency, and after a bit of furtling with HSBC's telephone service I discover that CGE haven't ever taken the original 127.85 out of my account, and they haven't contacted me to tell me that my Switch card hasn't worked or anything. Reluctantly I paid the debt collections people, and extracted a reference number from them to contact CGE with to complain.