Thanks to this forum and especially Omegod who went out of his way today to help me, when he didn't have to.
He messaged me the other day, to say his mate Tony, who is also a member here but not very regular, had a bag of bits including a sensor, and as it happens Tony lives about 5 minutes walk from me.
So I went and looked in the bag, and nothing that looked like a crank sensor.
Omegod, rang me, to tell me he was coming with a second hand one, and immediately drove from the other end of the m57.
He then borrowed my Jack and axle stand, and swapped it out. Apparently my having had a heart attack six weeks ago gets me special treatment.
It started first time. First time in 3 months.
I shall be getting a spare to put in the boot.
So thank you all, for the great advice, and especially Omegod for coming out of his way to help.