Lewis Hamilton improves with 1:38.183 but it is not enough to stop Nico Rosberg leapfrogging his team-mate into P1, the championship leader going a tenth of a second quicker.

Busy, busy, busy on the circuit now. The only ones not out on track are the two Williams.

A problem for Felipe Nasr now.

"Slow in, slow in, we have a problem," he's told. 

The Sauber, with medium tyres on, heads back in.

Eight minutes left and off we go, Lewis Hamilton leading out a train of cars.

Interestingly, it looks like pretty much everyone is going out on softs.

Renault and Williams' issues happened when they were on softs.

It looks like the sweeper has finally done its job because the session is due to restart in a couple of minutes.

Still red flag, by the way. There is a car with a large flat brush trailing behind it still sweeping up the back straight but there's a rogue piece of debris its missed.

Fortunately a marshal has spotted it and scampers on to the track to scoop it up.

Ten minutes to go.

Toro Rosso getting twitchy? Now their engineers are all stood around Max Verstappen's left rear.

Meanwhile, here's a something essential for any driver - sweets.

(or buttons, but I like to think they are sweets)

Image source, F1.com

Image source, Getty Images

No puncture on the Williams then, according to Pirelli.

Could it just be a truly bizarre coincidence?

The session is still red flagged as marshals deal with the debris on the back straight. There's plenty of people crowded round Felipe Massa's Williams in the Williams garage, with Massa himself stood behind them slurping from a drinks bottle.

Twenty minutes remaining.

Mark Gallagher
BBC Radio 5 live Formula 1 analyst

Very often a data analysis technician will spot something like a huge amount of braking and then realise something is up, sometimes they don't realise that he has hit the brakes because he had the blow out so it doesn't necessarily follow the way we hear it.

That team radio, by the way, was just before Kevin Magnussen's left rear gave out.

Kevin Magnussen team radio: "Possible problem with the brakes, be careful."

Tom Clarkson
BBC Radio 5 live commentator

Is it a car issue or a track issue? We don't know. I should emphasise we don't know the cause of the problem at the moment.

Red flagpublished at 03:58 British Summer Time 15 April 2016

03:58 BST 15 April 2016

And a left rear puncture for Kevin Magnussen as well, what's going on?

The Renault was powering down the back straight when the tyre blew out. Fortunately he is able to limp the car back, but there's debris on the track and the red flag is waved again.