Well the engine light did re-illuminate. So what Barnaby achieved by deleting the error code bought me an MOT certificate and time to investigate the problem at my leisure. I came across an extremely helpful website called Lambda Power, belonging to the eponymous company based in Sheffield. Contained within was a step-by-step guide to checking the state of the multi-named sensor sticking up just beneath the bonnet – o2, oxygen, lambda, airflow sensor – it answers to all sorts of designations.
Most of these steps involve removing it. Theoretically this is easy – it is just there, right in front of you and looking akin to a spark plug with an attached cable. But – although it has a hex base for undoing with a run-of-the-mill 22mm spanner, this is below the level of a heat shield, which is held in place by four bolts. It is easy to undo those bolts but it is impossible to lift the shield out with the sensor in place. It is deliberately designed this way to prevent have-a-goers like me from doing my own repairs. A special tool is required and it turned out that Screwfix stocks just such an item for twelve quid. Armed with this, some magic squirty stuff and a multimeter I proceeded to prove that this sensor was indeed kaput. A confirmation email to South Yorkshire, a credit card number supplied and the very next day a new sensor arrived - £79.95, manufactured by Bosch, branded Lambdapower, and postage paid. It took five minutes to fit. Leaving the vehicle for two hours with the battery disconnected helps it to forget what all the fuss was about. The light disappeared and six weeks later all is still well. Remind me to send an email of gratitude.
£800 from Honda? B*****ds!