Tea and sleep
In the late afternoon hours, many are reluctant to drink tea for fear of sleep problems. Let's see how we can harmonize tea and midnight's sleep.
Of course, not all kinds of tea influence sleep the same way, this depends on the theine content of tea. There are low-theine teas available (like the Chinese oolong or half-fermented teas) and tea products. Drinking these, you do not have to worry about sleep problems, what is more, they actually help you rest peacefully at night. 
However, you can also remove theine from any kind of tea. Certainly, black teas (especially Ceylon and Indian black teas) are more difficult to "trick" because of their high theine content, but those with a more sensitive body have to be also careful with green tea and Chinese flower teas.
Calmly, without theine
The most general (though not always correct) rule is that tea exerts its invigorating effect for some five hours. So, if you happen to drink a tea at five like our great British friends, you do not have to worry, it won't influence you by ten at night.
However, if you do not want to jeopardize your calm sleep at night, you should use more water for infusion. Pour hot water on the tea leaves, and pour it out after one minute (certainly only the water). Then pour some more water onto the leaves with the same temperature as the previous portion if you can, leave it for a while and drink it. This is a good method because the theine in tea gets extracted from the tea leaves most intensively at the moment of boiling, so by adding boiled water to the leaves several times, you can get rid of most of it.
However, note that your tea also loses a lot in its smell and taste this way since the harmony of these two comes from the balance of the quickly absorbing theine and the slowly oozing tannin.