Had an update from SEAT regarding the Leon kit.
Its still in the process of being evaluated as a UK product. Any aftermarket accessories offered for sale by SEAT in the UK need to be evaluated and tested here before they get the official sign-off, and of course get warrantied. That is despite them being official SEAT products in Europe. They have to undergo evaluation here because SEAT UK are ultimately responsible for offering the parts for sale in the UK.
The aftermarket parts people are testing it on several donor cars (press cars most likely) the current aim is for it to be an officially available product by January, but the order books may open before January. If I get a further update I'll let you know, but the dealers may know more in the coming weeks.