Thanks for this info Colin, really appreciate the reply!.... Not sure what the actual code letters/ numbers were (it was a "snap-on" diagnostic computer).... It was definitely bank 1, cylinders 1-3, so both sensors were changed, but after getting the car back, the fault returned.
Just heard today that all is well and it was an intermittant contact on the 2nd sensor (after the cat) connector pins, causing the fault to display. Mechanic has been excellent and can't wait to get it back tomorrow....£40 for lots of checks and peace of mind....priceless!
cheers 😎👍