Toyota did indeed have a replacement spoiler available, much to my amazement.
Collected my car on Friday, there is still a gap to either side between spoiler and the car, but having looked at the previous spoiler (dealer technician confirmed it was faulty), there are 2 strips of black rubber and not anything to stick it down.
Not sure if it's by design or a design fault, although having looked at
@Hachi-roku spoiler it looks much the same.
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They have made some minor damage to the paint work though. So it will have to go back in for them to fix that.
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And now the boot won't open from the button at the back - have to open it via the key. Hopefully they can easily fix when it goes back in.