Jonathan Agnew
BBC cricket correspondent in Cape Town

If South Africa start badly, they could really struggle today. There were some odd decisions at the start of the day. They look beaten. You feel England could run through them.

South Africa openers Pieter Malan and Dean Elgar out in the middle.

James Anderson to Malan first up.

It's down leg and Malan flicks iit round the corner for four.

Just the 434 more to go.

Adam Mountford
BBC Test Match Special in Cape Town

More on reports of illness in the South Africa camp. Cricket South Africa says that team doctor is taking extra precautions with all team members to ensure that it doesn’t escalate to the sort of level which affected England in the last Test.

I'm also hearing that the South Africa players joked on the last day at Centurion Park that after shaking hands with the England team they’ve never reached for the antiseptic fast enough!

Stuart Nelson: The 'come inside' wave that signifies a declaration is very disappointing. I reckon the captain should dab instead.

So South Africa need a Test record 438 runs to win the second Test in Cape Town.

Their captain Faf du Plessis once hit a majestic century as the Proteas made 450-7, chasing 458 to win, against India in 2013, with Dale Steyn and Vernon Philander opting to play safe for the draw instead of risk taking runs in a dramatic finale.

Can't see this South Africa batting line-up having something similar in them though.

Michael Carberry
Former England batsman on The Cricket Social

Sibley really set it up for the pyrotechnics of Stokes. It has put England in an unassailable position. The Test isn't over. Now the real work of taking the 10 wickets begins. South Africa are a proud nation and a proud people. Du Plessis has history in these situations. He won't lie down.

Jonathan Agnew
BBC cricket correspondent in Cape Town

I'm not sure about that session. What has it done? It wandered a bit. When Curran got out, they could have got out there to bowl. I don't think it will make any difference, they still have the time to win.

Dom Sibley leads the players off to a warm reception from all corners of Newlands.

An unbeaten 133, a supreme effort of patience and concentration and perhaps the first step of a long career at the top of the order.

But let's leave that for now, in the context of the game, Sibley has put England in a fantastic position to level the series at 1-1.

Ben Stokes smacked a brutal 72 off 47 balls and Joe Root made a fluent 61. Top batting.

Sibley reverse sweeps again, just a single this time.

And then Broad carts a slog sweep up in the air, no boundary but not out either.

Joe Root is hovering...

And there's the wave - England declare on 391-8, setting South Africa an improbable 438 to win.

Dom Sibley reverse sweeps for four!

All the gears.

Adam Collins
Australian journalist on The Cricket Social

We've got five days for a reason - there's no need to wrap it up in four.

Michael Carberry
Former England batsman on The Cricket Social

We expected this wicket to do a lot more. It has behaved pretty well; there has only been the odd ball that has done something.

Ben Stokes is trying to get Stuart Broad's attention from the balcony, with an arm movement that suggests, 'Just whack it, Stu!'

He duly tries, misses, then almost taps a short ball to short leg.

And then almost pops one up off the splice to silly point.

Joe Root has his head in his hands. It's at least never boring watching Broad bat.

Declaration watch: all the England players are now in whites.

There he goes! Stuart Broad connects with a sweep shot and bangs it away for four.

Andy Zaltzman
Test Match Special statistician on The Cricket Social

There are 150 overs left in the game...

Dom Sibley and Stuart Broad exchange singles off Kagiso Rabada.

The last time I can remember a declaration backfiring was when Joe Root did so late on day four against West Indies at Headingley in 2017.

England were 490-8 and it set West Indies 322 to win, which they did thanks to an absolutely stunning century by Shai Hope.

Even then, it still might've been the right call to declare - England wanted to keep James Anderson fresh to bowl and they just didn't bowl well enough.

Point is, the timing of the declaration doesn't seem to matter that much in the vast majority of cases.

Stuart Broad unfurls a few sweep shots but can't get a run.

That's a wicket maiden by Keshav Maharaj.

Momentum back with South Africa!

(I am totally kidding don't @ me).

Declaration watch: James Anderson has his whites on but no pads.