Undoubtedly – when used by the medical profession to treat people with kidney failure, anaemia and alleviate the side-effects of some AIDS treatments.

How fantastic.

It can also turn the blood to jam. A few years ago, there was a spate of riders dying mysteriously in their sleep. Cyclists’ superfit hearts can pump at around 190 bpm and then rest as low as 30 bpm. That’s when EPO can become lethal. The slower the heartbeat, the thicker the blood, the quicker it begins to clot and the heart begins to stall. That’s why I wanted to check if Didier was hanging off a door, stretching out to thin his blood. That’s why I needed to listen to his breathing pattern in his sleep.

And he was OK, so why not go back to bed?

True, Didier is sleeping soundly but maybe he’s taken a good dose of aspirin. The danger of taking anticoagulants to thin the blood is the risk of haemorrhaging should Didier crash.

Do you think Didier is on something?

I don’t know. I really don’t. The thing with EPO is that it must be taken up to a week in advance and then every couple of days. He wasn’t well, if you remember, towards the end of the first week of the Tour.

But where would he get it?

Shady characters and clandestine deals aren’t restricted to grim alleyways and crack cocaine.

We’re talking about a banned substance, not a class A illegal drug. Doesn’t pro cycling have one of the longest lists of banned substances in professional sport?

Yes. However, riders can spout the disclaimer ‘I’ve never tested positive’ – that’s different from saying they’ve never used dope.

But isn’t this the sport with the most dope controls and the lowest number of positive tests?

Some riders will always seek ways to stay a step ahead of detection. Ever heard of Michel Pollentier? In the 1978 Tour, after he had taken the yellow jersey on L’Alpe D’Huez, he failed the dope test by attempting to pass off someone else’s urine concealed in a rubber tube hidden in his shorts.

That’s actually quite funny.

Yeah, right – did you hear the one about the cyclist who went to dope control and was told, ‘You’ve tested negative and congratulations, you’re also pregnant’?

Oh, very droll.

EPO, however, is for the most part undetectable – it is virtually impossible to tell the difference between a rider who has a naturally high haematocrit level because he trains at altitude and a rider whose levels are high because he’s pumped with EPO.

Can’t a limit be set?

The UCI, cycling’s governing body, have set one. But somewhat arbitrarily. If a rider’s red blood cell count is over 50 per cent, he is forced to take two weeks rest until his level is lower.

That’s a start.

Hardly. Say Didier’s natural haematocrit level is 42, and say Luca’s is naturally 48 – Didier can legally dope himself to Luca’s level, to within a hair’s breadth of the limit, suffer no penalties and reap the benefits of an artificially stimulated performance from a prohibited substance.