Tell us about the pennies on the pendulum.

This is a two-second pendulum, and what we do to regulate the time is we add or take off old pennies onto the pendulum. If we take one off it slows the clock down by about four-fifths of a second a day and if we put one back on it speeds up by about four-fifths of a second. We’re allowed to be plus or minus two seconds a day, otherwise people start complaining. So this is how we keep the clocks timed. And is there a special stock of clock tower pennies? We keep a little secret supply of clock tower pennies which have been used for years and years and years. And we have a very kind lady sent us her collection of pennies as well, which we keep for emergencies only.

So they are not specially minted then?

No, they are not especially minted and we have looked through them to make sure there aren’t any expensive pennies in there!

How long is the pendulum?

Fifteen feet. And it goes from the suspension, all the way through the floor into its own little separate room downstairs. …and its swinging at what, two seconds…? Two-second beat, yes. Which is really relaxing if you listen to it.

 What's your job?

My job is Keeper of the Great Clock, which basically means I’m responsible to Parliament for the day-to-day working and management of the clock itself.

And what qualifications do you need?

 I’m a chartered mechanical engineer, ex marine engineer by trade, so I’m not actually a clock engineer.

 What causes the clock to stop?

There are two instances of the clock stopping. Well, there’s several obviously, but the common ones - if that’s the right word, because it’s about every 30 years - is snow freezing on the hands and we don’t seem to get those cold winters any more so that risk is reducing, but it’s always there. And the famous one with the flock of starlings that rested on the hands and stopped the clock and which I don’t think has been repeated since actually.

 When was that?

1949, I believe, yeah. Why it happened in 49 and hasn’t happened since I have no idea!

How often are the clock faces cleaned?

 Ah, I’m often asked that question. There is no set frequency is the honest answer. Roughly every five years. It was last done in 1999, just before the Millennium, so it’s actually one year overdue and we may well be doing it this August or we may do it another year.

How do you think the clock got its name?

Almost certainly the Commisioner of Works, Sir Benjamin Hall, yes. I think the prize fighter is a myth but it’s a very popular quite fun myth really but that is certainly my theory and I think it’s semi-official, shall we say.

 Didn’t it arise from a bit of heckling?

Yes, there was a debate in the chamber apparently which went on for some three hours on what to name the bell. And Sir Benjamin Hall got up to speak and apparently he was a very large man. And some wag got up and shouted out “Why not call it Big Ben and be done with it!” and the whole house fell about laughing and the name stuck.