I didn’t get round to sending the broken strap back, but I had decided that I really need to get back to fitness. As i had three bikes in regular use, a power meter would be pointlessly expensive for me and so i definately needed to train to HR. I bought a new Polar strap, with the intention of throwing the Polar sensor and fitting the Garmin one as recommended by web forums. Disappointingly, this still gave a high HR.
The penny finally dropped and I realised I must have some form of heart problem. I made an appointment with the doctor; well doctor appointments are apparently almost impossible, so opted for the earliest available appointment with practice nurse in four weeks time.