British airways seems to offer a flight in 2010 which leaves Boston at 8:15 am. Then you arrive in London Heathrow (LHR) at 7:45 pm local time the same day. In this way, you don't have to sleep in the airliner. Its with a Boeing 777-200ER and it takes 8 hours and 30 minutes. In 2011 this seems to be flight BA0238. The advice is to get up real early, but stay awake during the short day. As once you arrive in London, you need to go sleeping at an earlier time. The advantage will be that you don't feel a jet lag during days after your eastward transatlantic crossing. There seem to be few flights like this to Europe, but there is also one with United from Washington to London. British airways and American airlines also offer this kind of service from New York.

American Airlines seems to fly one of their Boeing 757-200 airliners at 8:50 am towards London Heathrow (LHR). This flight seems to arrive in London at 8:50 pm local time. It could be great if you don't want to sleep a short night on a plane over the Atlantic. Sleep at the Hilton Hotel within walking distance of the Boston Logan airport terminals and then have a day up in the air. Arrive in London around 9 pm. Go to your hotel there and have a good sleep again. 

Besides these daytime flights there are plenty more flight options with departure from Boston during the evening. For instance two daily British Airways Boeing 747-400 flights in 2011. And American airlines seems to have a daily 757-200 departure during the evening.
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