I think it depends when Tesla applied for the grant through the government portal.
Plug-in vehicle grant portal
See section on lead times
Lead times
3.9 We recognise that some manufacturers have long lead times and in this case the
order should be started as soon as a ‘contract’ has been signed with the customer.
3.10 A grant is not guaranteed until the vehicle has been validated through the portal.
However, provided that the vehicle is registered within 9 months from the date the
order is made, any claim placed on the system for a specific customer will be
guaranteed to benefit from the grant at the level advertised at the time the claim is
made.
3.11 OLEV will use its discretion to consider whether grant levels may be guaranteed for
vehicles registered beyond the reasonable timeframe. A claim cannot be added to
the portal before the contract with the customer has been entered into or after the
vehicle has been registered.
3.12 It is the dealer’s responsibility to track orders and ensure they are progressing
through the system by completing orders correctly. Orders that have been in the
system for more than 9 months will be entered into the ‘on hold’ status and will
require special dispensation from OLEV to be allowed to be processed