Answer
I have just booked my tickets for new york, flying in november. the cheapest were virgin at £257 return. you could get them slightly cheaper on ba but the return flight was at a ridiculous time in the morning so you would have to be at jfk for 6am.
i was very lucky, i tried to book via the virgin website but it was down so i called their telephone number and it was just really busy. i ended up calling after 10pm and getting through to the usa call centre. they quoted me £30 cheaper than the website cost! total win!
best times to book is either way in advance or last minute. this trip is a couple of months away but there was not very
any seats left on the plane!
also i would recommend using trip advisor as it searches all of the websites for you and gives you costs for each one in a separate web screen. i use trip advisor all the time
for reviews.