@Glos Guy I put in to extend for two years through my online account in January, and got the okay straight away, was not asked for mileage or adaptions. Not sure when these new rules came in, but I had no problem whatsoever.
Does the option to extend the lease only show on the online account once your order window opens? I’ve just looked at the online account, including the lease section, and cannot see any option to extend. The order window opens 22nd April so maybe it will become an option from that date? Knowing how rubbish their website and IT are, if they haven’t updated it to the new policy yet I might be able to do as you have done!