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Public Astronomer Dr Marek Kukula from the Royal Observatory in Greenwich said we are having a "leap second" today because the "earth's rotation is not a perfect time keeper".

He added that we have to introduce an extra second to our day because otherwise our clocks will "eventually become out of sync with the rotation of the earth".

Midnight will come later for the first time in three years tonight as an extra second is added to the official time set by atomic clocks. The "leap second" means the last minute of June will have 61 seconds in it.

This clip is originally from 5 live Breakfast on June 30 2015.