This sounds like a radio-controlled clock. They all seem a bit rubbish, now, the UK ones that rely upon the
NPL signal from Anthorn (they all appear to have become less reliable, ever since they moved the transmitter from Rugby).
Or, equally-possible, you may have a worn cog (the clock, not you....well, maybe you, too). Here's the procedure to prove this.
Put a new battery in the clock. Turn the clock UPSIDE DOWN, such that 12 is at the 6 o'clock point, 6 is at the 12 o'clock point, and the numbers 3 & 9 exchange sides. Set the clock to the correct time BASED UPON THE SHAPE THE HANDS MAKE. Leave overnight, and check whether the clock is still telling the 'right' time. If it is, you need to somehow revolve the mechanism 180degrees relative to the dial, and hey presto, sorted.
One thing to worry you about.....remember how you were told, as a child, that if you broke a mirror you got seven years bad luck?
Do you remember the bit when they told you that if you ever throw-out a broken clock, time everywhere just stops? That's irregardless of whether your clock is an atomic-synchronised diamond masterpiece built in a Faberge egg, or a cheap quartz movement stuck in the middle of a recycled 45rpm single record in your Gran's loo. Never throw away a faulty clock....it brings bad times. Either fix it, or give it away.