Thanks everyone - problem solved by my son. He put in a more closely speified query into Google and got a result.
I think the EPG disappeared, not when my (Oxford) transmitter went digital, but when the last one in the UK changed over.
When I select "Guide" on the remote, I get a message "this function cannot be used now"
Contacted Sony customer care (in Cairo!) who suggested updating the firmware from the original 1.65 to 1.70.
Done this, but no improvement.
Not related to digital switchover because it was working fine...