Thanks for the advice.
Still no further on. Virgin have again told us that we can fly from Heathrow to Washington / LA / San Francisco on the date we want to travel, but they will not help with any onward connection. They have also offered to give us lounge access.......
The CAA advice is that the contract with Virgin is that they are responsible to get us to the final destination that we have booked.
BA do have a direct flight on that date, but again,Virgin have told us that they will not book us onto that flight, as we can fly with Virgin to America, just not the destination that we have booked.
The annoying thing is that the CAA will not get involved for 28 days, to give Virgin time to "do the right thing" (there words, not mine) by which time the flights from San Francisco will be more than $49, so still not sure how to play things.....
Thanks again