Phew, it's passed!
I fitted a NGK NTK OZA527-E9 sensor and it flew through the emissions test.
I had trouble getting the old sensor off though. To get through the test initially, the advise was to make sure there were absolutely no leaks in the exhaust system. So I used exhaust paste on the lambda threads, which meant it was pretty much welded in place. I broke a spanner trying to get it off. In the end I cut the lamda with an angle grinder and then hammed a socket onto what was left of the nut and used a breaker bar.
Anyway, I'm pleased to be back on the road. Hopefully get a few more runs in before winter sets in.
Cheers
James