http://news.bbc.co.uk/1/hi/business/6272606.stm

"London Underground said that fare dodgers will still be able to use
cheques to pay their fares, and fines, to ticket inspectors".
So only a fare dodger can pay by cheque. If I happen to lose my
ticket or I am mugged will I have to find some other means of payment
or would I become a fare dodger.

Kevin