Take out Amex Platinum (£450 fee), use the link at Quidco for £50 cashback
Claim your Cathay Pacific Gold card which gives almost all the benefits of BA Silver inc lounge access for a year
Cancel Amex Plat and get your £450 back, so you are £50 up as well? Your Cathay Gold remains valid for the full year.
There is an optional stage whereby you spend £2000 on the card before cancelling and get 3o,ooo Membership Rewards points as well