Tim+ wrote:

Our earthing system seems to be a wide metal braided strap attached to the
incoming mains cable. (Looks like a lead sheath on the incomer.). Is this
okay?

You need to read the regs on car charging and earthing (see John Ward's
youtube videos) unless you have a very fancy charger that can detach the
earth in fault conditions, you probably need a separate earth rod for
the car and not to connect it to you main earth.