The fast of 10 Teves commemorates the siege of Yerushalayim. It is a day of mourning, on which we remember the attack launched by the Babylonian emperor, Nebuchadnezzar, and his army. Although the siege was not a punishment for this generation, we mourn because it is said that for every generation which does not see the temple rebuilt, it is as if they destroyed the temple. And so, in this way, it is our responsibility to fast.
In London, England, the fast starts on the morning of January 8th, at 6:19 AM. It ends at 4:51 PM. If you intend to eat before the fast begins, please have this in mind before you wake up! I wish all those fasting an easy fast. May we soon merit to see the rebuilding of the Temple, and the arrival of Moshiach, speedily and in our days!