Thank You for your recommendations. As it happened I was able to borrow one from a friend. It was a TOPDON Artilink 500B which did two jobs. First it showed up that I had a faulty Nox sensor, which the garages wanted nearly £900 to replace, (was able to obtain an Original Equipment one off eBay for £289, which cleared the fault) and secondly, it has a battery test function which showed that my battery was well underpowered( original, so well over 7 years old) which I have replaced.
