Dom Joly: Lobsters, Serena and a glum Sir Cliff

It's been a crazy week – I've been ensconced in the bowels of Wimbledon working for Radio Five Live. In between long periods in a tiny booth on Centre Court I have mainly been patrolling Henman Hill, or Murray Mount/Mound/Mountain.

To add "colour" to the tennis coverage, interviews with spectators on the hill are deemed necessary and I was the muggins to do it. I dreaded the daily approach – the drunken jeers, the stumbling through bright pink lobster people often lying motionless on the floor. Then the questioning: did people support Murray, did they think he would win, should he steal the hill off Henman, might he actually smile once?

The heat was incredible – for a while I took refuge in a walk-in fridge behind the Pimm's stand: it was sheer heaven. I got chatting to the Pimm's workers. They sold about 500 glasses of Pimm's every hour. If you assume that they were there for about seven hours on average with the Pimm's at a staggering £6.50 a glass – that's about £22,000 a day, just from this one stall.

Wimbledon in general is frighteningly expensive and is definitely not the place for a cheap day out.

My biggest surprise was just how amazing the semi-final between Serena Williams and Elena Dementieva was. If I'm honest, I've had very little interest in the women's game. I laughed when Alan Davies was asked whether he was disappointed to have been invited to Wimbledon on Women's quarter-finals day. "Yes," was his short and truthful answer.

Normally the men's game is just infinitely more interesting and watchable. Not so with the first semi-final. From the word go it was totally electric – I have never seen women hit the ball so hard and the whole match never dipped for a moment. I had a sneaking suspicion that Serena would get through as there is just that air of invincibility about her. I even tried to get on to Betfair to bet on her winning when she was facing a match point against her – sadly I couldn't work out how to do it. I'm a bit rubbish at betting, luckily.

The sheer difference in size between the two players was extraordinary. Serena is built like a stout tree and stomps around the court screaming at herself in quite a frightening manner. The Russian, on the other hand, looked so slight that I was worried that a freak gust of wind might blow her off court. Whenever things weren't going well she'd look up to her mother in the player's box and scream stuff in Russian at her. Unfortunately the mum never shouted back which would have been very entertaining. I don't know why she shouted at her mum so much as she looked like a very sweet lady.

Personally I'd have had a go at Cilla Black and Sir Cliff Richard who were sitting in the front row of the Royal Box. Sir Cliff looked very glum – he knows that the All England Club have spent a hundred million pounds on the new roof just to prevent him from ever singing again. I remember the buttock-clenching embarrassment of that moment when he picked up the wireless mike and led the crowd through "Summer Holiday." It must never happen again and the Club made a very wise move in installing the roof, whatever the cost.

If the roof hadn't been there then we could have faced the nightmare prospect of a Cliff/Cilla duet ... imagine the scenes – them both belting out the theme tune to "Surprise Surprise." Actually, I would pay to see that but only if we were allowed to fire tennis balls at them with a machine.

My booth got really hot and I slipped out into the Centre Court and plonked myself in an empty row of seats. I was immediately pounced on by a large Air Force man – he told me that I couldn't sit there. "Why?" I asked him. "They've been empty for the whole match." The row was for "honorary stewards" he told me. I have no idea what an honorary steward is but they're certainly not interested in tennis as the row stayed empty all through this amazing match. It's criminal to have these empty seats when people queue all night just to sit on the hill watching a huge screen.

It's not as bad as the cricket though, which has large swathes of empty seats as the corporate clients gorge themselves on complimentary Coronation chicken. The only sport this week is my girl's rounders match – it's going to be a comedown.

Off the Wall contest? That'd be a Thriller

I think I detected a secret competition among Wimbledon commentators to see how many Michael Jackson song titles they could slip into the commentary. It might just have been my imagination though.