GB in fourth place at the moment. It's very tight though...

Nigel Levine looks a long way back but he's in lane one and the exaggerated stagger makes it confusing.

Delanno Williams is on second leg for GB. 

Ah, Trinidad and Tobago have been disqualified from that first heat, after finishing in the third automatic qualification spot. That could be good news for GB - if they get through.

Here we go then. Nigel Levine goes first for GB, Martyn Rooney on the anchor leg. He was not happy with his run in the individual event - as you may recall...

DefiantZombie: how do pole vaulters get their poles to the event? you never see anybody carrying them on the train or strapped to a clio roof.

GB's female 4x400m relay quartet have been talking to BBC Sport's Phil Jones after qualifying for Saturday's final:

Emily Diamond: "I found myself more nervous today than in my individual race because I didn't want to let the girls down."

Anyika Onuora: "I've been watching the rest of the team perform and was waiting for my time to step out into the Olympic stadium. It was great."

Kelly Massey: I have a lot of experience of running the relay and was determined to hand over in second place."

Christine Ohuruogu: "We have a strong medal chance but we are trying not to get too excited."

Image source, AP

Just an hour now until the final. Will this man be Olympic champ?

Jamaica finish fast and take it on the line, the US second and Trinidad and Tobago take the third auto spot. Botswana were flying after two legs but faded badly. 

You will not be surprised to hear that the US are winning this first heat, with Botswana on their heels.

Holly Bradshaw, second attempt at 4.60m - OVER!

Made it look easy. Well in. 

Redmond, Akabusi, Regis, Black.

The world 1991 4x400m relay final was a top class event. How will the class of 2016 get on? We will see the heats tonight and GB go in the second. Drawn in lane one. 

Image source, PA

The atmosphere is building nicely ahead of Lutalo Muhammad's gold-medal match, according to Nick.

Great Britain finish second in their relay heat with the fourth fastest time overall to qualify for the final. Job done for GB!

And number nine may not be far away.

Great Britain's men go in the second heat (01:20 BST). The team picked tonight is Nigel Levine, Delanno Williams, Matt Hudson-Smith and Martyn Rooney. 

A cast-iron favourite, dominating your sport all year - and then you don't make the final.

It's a living, breathing nightmare for hammer thrower Pawel Fajdek. So dominant has he been in 2016 that each of the top 10 throws all belong to him.

But in qualifying he threw a mystifying 12m short, external of that form and crashed out. 

His absence opens the door for Ivan Tsikhan and defending champ Krisztian Pars.

Image source, Reuters

Holly Bradshaw dislodges the bar on her second height of 4.60m - but she was well clear of it! Well over, but then she knocked the bar off with her knee on the way down. 

2Pac. Ray Charles. Al Green.

When Michael Johnson was on Desert Island Discs a few years ago he brought his A game.

Well worth a listen...

The United States dominate the first relay heat to qualify for the final alongside Ukraine and Poland. 

Jamiaca win that heat by a mile, Christine Ohuruogu anchors Great Britain home safely in second place, and Canada are third.