Good old spi emissions issues - usual story, fails MOT, found split vac pipe elbows. Replaced all those, check on code reader and lambda not switching, constant 1.8V.
New Bosch lambda fitted and still get a constant lambda reading of 1.8V. Also given it a full service.
All other readings are as to be expected, coolant temp, MAP etc. Have changed lambda heater relay and tested that is getting 12V at the plug. If I pinch the fuel supply line just the right amount to lean it off the lambda starts switching as it should so proves it works. It runs and drives very well which is not what I would expect with a lambda reading of 1.8V!