Wow Grumpy - that is awesome help, especially given my lack of savvy blush
Thank you kindly for your welcome. Cranky welcomed by Grumpy... cool!
It is the wheel drive - it is constantly engaged.
The first problem was the drive belt for the cutter deck came off it's runners - I put it back on twice, noticing that it was fairly badly worn and damaged, and therefore need replaced - thought I would persevere just to finish the garden.
Then the wheel drive clutch stopped having any effect - just constantly moving. As the brakes died 15 years ago I use reverse as brakes so I decided it was too dangerous to carry on.
Now that I've calmed down, I'll give it a thorough clean, and then see if I can glean anything from the charts you have provided - thank you VERY much indeed!!

I will let you know how I go!

I had such a bad-equipment day yesterday, brush-cutter #1 that I had just serviced, conked out, brush-cutter #2, a cheapy that a neighbour gave me, ran out of twine and the nut holding the twine holder was locked tight. Then the mower played up, lol
I went inside and Wifey was swearing at her printer which had also died - the planets must have been aligned in a middle finger formation!! laugh