To prevent the disruption in your body's timing that comes with crossing time zones, you need to change your body's clock sooner rather than later. You can do this by putting yourself on the same time as your destination time zone before you fly. If you know you'll be traveling to London from the Eastern United States, you'll have a five-hour time difference to cope with. Plan for it.
Get your body used to London time the week leading up to your flight. Wake up and go to bed at your normal time as if you were in London. It would be three hours later than what you're used to, but it'll help your body adjust. Don't feel the need to do it all at once. Work up to the time difference gradually -- perhaps 30 minutes each day. Your body needs to stay within its daily regime, or it starts to fight the effects of jet lag. If work doesn't allow you to make this type of adjustment, do what you can to try to get your body's clock adjusted to your destination's time.