Motability have posted an article about the grant on their website. Link https://news.motability.co.uk/scheme-news/what-does-the-electric-car-grant-mean-for-me/ Looks like they are leaving it to manufacturers to make any offers in the next quarter from a cursory read.
Exactly as I thought. The two key quotes from the article are;
If a car qualifies and it’s available on the Motability Scheme, it’s up to the manufacturer to decide if they want to change the Advance Payment.
and
If a car becomes eligible for the grant, it will not necessarily mean the Advance Payment will change. This is subject to the manufacturer’s discretion. In many cases, as we update our prices every three months, the best possible deals have already been applied for Scheme customers and won’t change until they are reviewed again next quarter