Paul, It was the shortest way home! Also I would be able to get a good measure from 8k to the finish and even with a reduced accuracy 7k to 8k interval I am now able to let the race director know quite closely where the start/finish line needs to be.
Gene, The SPR is a very good point. I was following the race director on his bike so I knew that I was not going to need to actually swim. However he rode closer to the road centre than me. I took a line as close to the hedge as I deemed prudent, but I was worried that there might be a ditch or some other problem hidden in the brown water, and I remember picking a line just a little further out to give me some margin to ensure I was not pitched off the bike into the water. You can see some grass of the verge in the picture and I may be 1 metre outside the SPR and so riding a longer distance, fortunately the total angle of the bend in road is not very large over the flooded section, so I have still got a reasonable overall length measurement, assuming of course that the constant changes by less than the 1% change which occurs when I get off the bike and push it.
1% constant change would give 2m over 200m, and so my provisional start/finish result is probably within the SCPF. But has anyone ever taken a course under water calibration?