And that is my race run for the day, and, just like Mark Cavendish, I'm retiring a few stages early. Thanks for all your comments and company. It's been another great day for British cycling. 

The race report is live and will contain more reaction to today's victory.

Alistair Magowan will be back tomorrow to take you through stage 19.

Be sure to join him.

So, on to Friday's stage 19.

It's the third of four days in the Alps. There are four mountains to negotiate, not to mention the descents.

Chris Froome suggested a little earlier that thunderstorms are forecast which means this race could well be far from over. 

Pre-race Geraint Thomas picked it outs as "a dangerous stage". Find out why in his Tour stage-by-stage guide.

1. Chris Froome (GB/Team Sky) 77hrs 55mins 53secs 

2. Bauke Mollema (Ned/Trek) +3mins 52secs 

3. Adam Yates (GB/Orica) +4mins 16secs 

4. Nairo Quintana (Col/Movistar) +4mins 37secs 

5. Romain Bardet (Fra/AG2R) +4mins 57secs 

6. Richie Porte (Aus/BMC Racing) +5mins 00secs 

7. Fabio Aru (Ita/Astana) +6mins 08secs   

8. Alejandro Valverde (Spa/Movistar) +6mins 37secs

9. Louis Meintjes (SA/Lampre) +7mins 15secs   

10. Daniel Martin (Ire/Etixx - Quick-Step) +7mins 18secs 

Adam Yates has just been on the  podium to pick up his white jersey as best young rider. The 23-year-old from Bury is still third overall, but Nairo Quintana is just 21 seconds back in fourth.

Here's what he had to say: "I was strong at the first time check and then my legs fell off. I did the best I could. I didn't lose too much time. I've got two more days to fight and we'll fight for every second. 

"It's going to be a big fight for the podium."

Chris Froome is currently collecting another yellow jersey, another bunch of flowers and another cuddly lion. Today was the 54th day that Team Sky have spent in yellow. I wonder who gets all the lions?

Here's a few more words from the great man: "We have two more big days to come, hopefully I didn't leave too much out on the road today. But I'll be giving it everything to get the job done. 

"Tomorrow is a very tricky stage with tricky descents and there is talk of thunderstorms. We cannot relax and switch off."

The briefest of interviews with stage winner and race leader Chris Froome: "I really didn't expect to beat Tom Dumoulin. Pacing was key. I started steady and controlled the first part and then really went for it over the top. I'm really happy with that."

If you want your speed stats, here you go...

Not quite out of sight Mark, but not far off, after a masterclass in time trialling.

There was a big smile and a punch of the air as Chris Froome crossed the finish line. And this is why...

So that is a seventh stage win of this year's race for a British rider - four for Mark Cavendish, two for Chris Froome and one for Steve Cummings. Sensational.

But more importantly, Froome's overall lead is going out way above three minutes by my reckoning.

Chris Froome times his rider to perfection, to win the 17km time trial in 30 minutes, 43 seconds. He finished 21 seconds quicker than Tom Dumoulin.

The Dutchman gave a wry smile as he watched Froome cross the line before vacating the winner's chair that he had been happily sitting on for around two hours.

Team Sky's Chris Froome wins stage 18

Rob Hatch
BBC Radio 5 live commentator

This is increasingly looking like the day that Chris Froome retained the Tour de France.

Just the technical lefts and rights to negotiate for Chris Froome. Rob Hayles wants him to back off and relax and just get to the finish line now.

But he is stomping all over those pedals.

Bauke Mollema is losing time on Adam Yates but maybe only a couple of seconds. I need to wait for official confirmation but it could be as you were on the top three.

Here come's Froome...

Finally the Tour computer updates, Chris Froome was just 10 seconds down on Tom Dumoulin after 10km. Phew.

And at 13.5km he has gone 13 seconds quicker than the Dutchman. Stage win number seven for British riders?

Bauke Mollema is the only other man out on the road. And he is coming into the finish line...

Adam Yates loses a bit more time in the third section and is 52 seconds off the pace set by Tom Dumoulin. Bauke Mollema is rocking and rolling all over his bike.

Yates is powering to the finish line. He is under the Flamme Rouge, no pedalling as he negotiates a left, back on the gas out of the corner and then out of the saddle to power over the line. He finishes in 32 minutes, six seconds, 62 seconds behind Dumoulin.

Has that hurt his podium ambitions?

Oli: Did a 10 mile TT on Tuesday, 26:47. Not bad for no aero gear and only my second time trial

Christopher Wright: Took a wrong turn on the club10 a few years ago, ended up doing an extra 5 miles! Suffice to say not the quickest time