I got a new electric mower today - Bosch Rotak 430. I am puzzled, very
puzzled, by the manual that comes with it, concerning extension leads.
It says "your machine is double insulated and requires no earth
connection". Protection class is II.

Yet, when it describes extension leads, it says "Note: If an extension
lead is used it must be earthed and connected through the plug to the
earth cable of your electricity supply..."

That makes no sense to me. Is it just a ****-up? They've copied a bit
out of another manual for a machine that is earthed?

This matters a bit, because I'll need probably 40m of extension cable
and the extra cost and weight of an earth wire is significant. I should
be okay with 1mm2 2 core cable.

Also, they recommend that for up to 40m of cable it is okay to use 1mm2,
whilst for 40-60m they recommend 1.5mm2. Is the voltage drop down an
extension cable so large that it significantly affects the mower? Or is
this just more elfin safety nonsense? The mower is rated at 1800w.