I am retired, obviously, so I have too much time on hand.
Just went on Expedia.uk and tried a search LGW-LAX. It
returns NWA at 385 pounds, AA at 450, DL at 465, US at
435, CO at 623. Same search LON-LAX added UA at
500, AA at 435, then Virgin at 490. A search LHR-LAX did not
show NW, only UA, AA, BA and Virgin. Searched the dates
you provided. By the way a week later saves you 80 pounds.
But maybe I was just lucky. Anyway, please try again.
And, Spinzcity, thanks for the car rental info. I will try that
with AutoEurope. I have used them a couple of times from
their US website. I would be terribly upset, if I overpaid.