Just putting this here for others. As you say, the Seiko Boutique in Knightsbridge has the SRP777 in stock for the full £379 but it's the "international market" SRP777K1 and not the made in Japan SRP777J1. Also, you have to go to Knightsbridge to get it :-/
Copied you. Bought the PADI Turtle for £297.99 from Lowry Jewellers. Only £5 more than a Chrono24 seller in the Netherlands, but is also £130 off RRP, which is what everyone else is still selling them for.
Just putting this here for others. As you say, the Seiko Boutique in Knightsbridge has the SRP777 in stock for the full £379 but it's the "international market" SRP777K1 and not the made in Japan SRP777J1. Also, you have to go to Knightsbridge to get it :-/