The leaders go over the top. Romain Bardet nips off to the right of the road to collect a rain jacket from a soigneur.

Back in the peloton, Bahrain-Merida continue to lead and Vincenzo Nibali is right at the front. So is Alberto Contador, dancing in his pedals, in familiar style. They reach the summit 90 seconds adrift

Let's go descending.

This just in from BBC Radio 5 live's Gemma Sterba: "It's raining so hard that you can now count the number of spectators on one hand. It's such a shame because normally the finish would be packed with fans on what could be such a historic day.

"As for the Froome, Froome, Froome signs we saw on the way up, they're long gone."

The leaders are 1km from the summit. British twins Adam and Simon Yates are in a group that now totals 11 and still features Romain Bardet.

Their lead is around 90 seconds over the peloton.

Has the FairlySecretCyclist blown us all out of the water straight away? Looks tough but what about the gradients? Anything approaching the 24% on the Angliru? Cracking effort though.

If you can rival that...#bbccycling

And as I typed that, the Bahrain-Merida team of Vincenzo Nibali assembled themselves at the front of the peloton.

Chris Froome, alert as ever, drops in behind the Italian. He will not want to give the Italian an inch over these next couple of kilometres to the summit.

And let's not forget, what goes up...descending in conditions like these are going to be treacherous and that's where it will get interesting.

I'm sure Vincenzo Nibali won't want to win the race if Chris Froome slides off but the Italian is the better descender and he will likely push harder than the Briton and test his nerve.

Froome has improved his skills going downhill but will he have the bottle to follow?

The peloton almost grinds to a halt as it hits the steepest slope the Alto de la Cobertoria has to offer. The 18% ramp is only a precursor to what is to come though.

The breakaway group is also finding the going tough. Dimension Data's Igor Anton gives the passing camera bike a wave as he slides backwards.

There are still 3.5km remaining to the summit.

The rain is falling as the riders make their way up this first climb. A few brave souls are chancing their arm and darting off the front of the peloton.

The official Vuelta website suggests the rain will continue to drop from the sky until they reach the Angliru, when the sun will come out. I'm not sure who is doing their forecast but our reporters on the ground beg to differ.

Meanwhile, five riders are trying to ride clear of the breakaway...

Tom Fordyce asks a question: "Is the Angliru the hardest climb in cycling? Even driving up it earlier today was nightmarish - a relentless steepness, brutal ramped hairpins, the smell of burning clutch in the nostrils. This was a cattle track until the start of the century. Even now the tarmac is hanging on for dear life."

So, have you ever ridden anything more severe? And I want pictures...#bbccycling

The road has finally gone properly uphill. Team Sky, Trek Segafredo and Katusha are the teams setting the early pace in the peloton.

Their work has pegged the escape back to one minute. Seven kilometres to the summit.

Nadine Waters and Mark Spittlehouse from Guiseley had been walking for three hours and 14 minutes, precisely, when they were snapped by our Gemma.

Just the 500m to the top...if you are out there, either track down Gem and Tom, or send in your pics via #bbccycling

Image source, BBC Sport

The 18 escapees are now 90 seconds up the road. There are several riders in it who will fancy a tilt at winning today's stage.

Not least the Yates twins. Adam and Simon ride for Australia-based Orica-Scott and came into the race as team leaders with Colombian Esteban Chaves.

With the red jersey now out of reach, it's time to try and salvage a stage win.

But will they stay clear on this first climb? We are fast-approaching the bottom of the mountain.

It looks quite nice and sunny down in the valley as the riders continue to wind their way towards the first big climb of the day. Up on top of the Angliru and Tom Fordyce is feeling the pain.

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Jon France: #bbccycling, external#LV2017, external Contador should be consigned to history and forgotten about... @FabioAru1, external has a lot to prove today, maybe a stage win?

Image source, AFP

Yep, half the stage is over already. But it's about to start getting tough. The three categorised climbs are all squashed into this second half.

We start with the category one ascent of Alto de la Cobertoria - an 8.1km climb with an average gradient of 8.6% and sections at 18%. Looks fairly straightforward in comparison to the Angliru!

Our 18 out front are still one minute clear. Ireland's Nic Roche is the highest-placed rider on general classification at 14 minutes, 54 seconds behind Chris Froome.

Liam Watson: "As much as I want Froome to the win the Vuelta it would be brilliant to see Contador bow out with today's stage win. #LV2017, external#bbccycling, external

You may get to see both Liam.

Italian Vincenzo Nibali, another one of the six to win all three Grand Tours, is the rider most likely to nick the leader's red jersey from Chris Froome.

Before today's stage he said: "It's a very difficult stage and the weather is going to be shocking. It will be explosive. It's an incredibly hard climb with some huge percentages from the beginning."

When will Nibali go on the attack? How does he best surprise Team Sky and Froome? #bbccycling for your thoughts...

Image source, Getty Images

Matt Taggart: "When I first saw the profile for stage 20 I thought my graphics card was knackered. That last climb is insane." #bbccycling

Alberto Contador does have form on the Angliru. He won here in 2008 on his way to overall Vuelta victory.

The mountain has only featured in the Vuelta six previous times but has already reached legendary status. It is where Bradley Wiggins lost the race leader's red jersey in 2011 to Juan Jose Cobo, who would go on to win the race.

Wiggins would finish third overall, behind then Team Sky team-mate Chris Froome who recorded the first of his three runners-up spots. In 2002, fellow Briton David Millar's protest over the difficulty of the climb led to his disqualification from the race.

The 13.2km ascent has an average gradient of around 10% with sections at 24%.

Alberto Contador is a three-time winner of this race and is one of only six riders to win all three Grand Tours - the Tour de France and Giro d'Italia are the other two.

The 34-year-old, who has won seven Grand Tours in total, is retiring after this race.

At more than three minutes behind Froome he's probably too far back to mount a challenge for the title but you can bet he's told his team he wants to be in with a chance of winning today.

And who would begrudge Bertie a final win?

Image source, EPA