Thanks for your replies - I am in complete agreement with the comments made! Needless to say, I did not choose the item in question but it has landed with me for repair!
However, a couple of thoughts are as follows:
(1) In the UK, goods are required to be 'fit for purpose' in relation to a reasonable expected working lifespan. In spite of the statutory 12 months guarantee period there can be a period of up to 6 years when a claim can be made for a faulty item. Has anyone any experience in making such a claim?
(2) The battery seems fine (and is charging) - the motor and switch are also working. It would then seem possible to simply bypass the controller board and run the unit at a fixed single speed. There is nothing on the controller board which looks damaged or over-heated - I still think the board looks way over complicated to simply run a motor!
Thanks to all.