German premium brands rely heaviliy on sales within the US market, as such they could choose to increase price’s in other markets, to offset losses from US tariffs.
Overall its unlikely to impact the scheme, other than some possible tail end AP increases based on above. @Brydo touched on a good point, with the US blocking China coupled with Rach from accounts adding luxury car tax to EV’s, China could see this as an opportunity to push more cars cars into the UK, at below the luxury threshold, which could offset any attempted price increase by EUrope manufacturers, who might choose to increase prices on their entry level cars to try and offset losses from tariffs applied by the US.
I don’t think any cars on the Scheme are actually US built, even Fords bigger pickups such as the Ranger is built and shipped from south Africa.