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 :-/
Anyone know where in the UK I can get a Seiko SRP777?