Steve Daws: Graeme Smith on TMS is superb, real knowledge/insight. Much prefer him in the comm box than opening the batting against us too.

Umpire Dar whips out his light meter (apparently it's named Megatron, after the Transformer), Toby Roland-Jones takes his sweater off as if he's going to bowl, puts it back on (tick tock, goes the clock) and instead it's going to be Ben Stokes switching to the Pavilion End - he's going to bowl round the wicket to the left-handed Rabada, who knocks a single to mid-wicket. Bavuma, who was taking singles at will against the spinners, looks to be digging in for the close.

Jonathan Agnew
BBC cricket correspondent on TMS

It has been a funny old advert for Test cricket this series so far, we've had two four-day matches with both teams batting horribly

I'm no lip-reader, but I think Messrs Root and Dar have just had a "is the light good enough to bring back pace?" "No, not just yet" conversation. In the meantime, South Africa keep plugging away against Moeen Ali - while an uncharacteristic fielding lapse at mid-wicket by James Anderson gives the Proteas an unearned single. Four singles from the over - spin is not working for England.

Rabada reties his shoelaces between overs, and with little wicket-taking threat from Root's off-spin, South Africa are increasingly confident in picking off these singles to chip away at the follow-on target of 154. Hang on, was that a drop? Rabada drills Root back to the bowler and he can't hang on, but it was a bump ball.

Dan Norcross on TMS reckons the light is improving - possibly enough to ask the umpires if they can bring back pace.

Image source, Reuters

Seb Poznansky: Hopefully England fans won't be fickle enough to lambast Roland-Jones on his current slump of over an hour without a wicket.

nicklindsay: Just wondering why TRJ has no cap number on his shirt? Did his Mum forget to embroider it?

Mike: Floodlit Tests can take place at night. So what's the problem here? Lights on, get on with it.

As expected, it's Moeen Ali, he of the shaven head and beard, to bowl from the Vauxhall End. Bavuma guides a single to fine leg, Rabada adds a couple of leg byes, then drills a quick one to mid-on - an awkward little partnership (from England's perspective) is now worth 27.

Richard Cross: England playing very good in this Test, what's the betting they will be awful in the next Test.

Totum: TRJ now my second favourite Toby, above Jug and tucked in just behind Carvery.

James Wurr: If Philander doesn't return to bat before end of innings is he out retired hurt or is he timed out? Workplace argument ensuing.

He would be listed as "absent hurt" or "absent ill".

Root tosses the ball from hand to hand, with a slip and a short leg in place. Bavuma watchfully leaves a loopy short ball alone before tapping a single to long-on. Rabada straight-drives a two past the bowler - and South Africa have avoided their lowest score since readmission to Test cricket.

Graeme Smith
Ex-South Africa captain on BBC Test Match Special

As tough as it is going to be, I'd almost want to follow on as a batting unit because it gives me an opportunity to get us back in the game.

As umpire Aleem Dar takes a light meter reading, Moeen Ali is summoned to bowl - we may be at that stage where England have to bowl spin if they want to continue playing tonight. And, as Graeme Smith suggests on TMS, if they get after Moeen, England can always turn back to a seamer and they'll go off.

In fact, it's not Moeen Ali - as if they're saving Moeen to bowl from the Vauxhall End, Joe Root is going to bowl himself. That means close fielders, who require helmets and shin guards, and we've wasted a good two or three minutes already. Careful you don't get yourself an over-rate suspension, Joe...

Image source, Reuters

Ed Smith
Ex-England batsman on BBC Test Match Special

I find it is becoming increasingly clear than when the arm wrestle is going one way it goes more quickly.

The umpires have had their first preliminary chat about the light. It's been all pace from England in this innings, Stokes continuing from the Vauxhall End and Bavuma still picking off singles when he can. Rabada tries to turn a single to leg, the ball flies off a leading edge between gully and point, and away for four.

Ed Smith
Ex-England batsman on BBC Test Match Special

What makes Test cricket so special is the drama of a close finish after four or five days. That is our USP and if we don't have that something is disappearing.

Bavuma picks up a leg bye when Anderson strays down the leg side, and Rabada remains stout in defence. Maiden over.

And after an over with vice-captain Stokes in charge, Joe Root is back - he's got his instructions from TB, if that's what he went off for.

Graeme Smith
Ex-South Africa captain on BBC Test Match Special

The follow-on is something Root has got to do. Vernon Philander is not even at the ground, he is still at the hospital, so England are two wickets away. Rabada has potential to become a lower order all-rounder, maybe not of the Ben Stokes kind but then he is probably more of a bowler than Stokes.

Stokes to Bavuma, the little right-hander squeezes a two to Moeen Ali on the point boundary, while Rabada shows all-round potential with a well-driven four through the covers.

The unmistakeable figure of Neil Mallender, fourth umpire in this game, emerges from the pavilion - possibly wielding a light meter which may come into play in the next hour. And Joe Root nips off the pitch - surely he doesn't need to ask Trevor Bayliss whether he ought to enforce the follow-on?

Tim Ellis: Is this enjoyable? When are we going to get a tense game rather than a one-sided one lasting three and a bit days?

Critchley - Author: There's something very Angus Fraser about TRJ... a bit handier with the bat mind.

Jack Taggart: Importance of Cook's innings can't be underestimated. Got them through a tough time and allowed Stokes to show his true class.

Graeme Smith
Ex-South Africa captain on BBC Test Match Special

We said early on that is didn't do that much early in the morning but England have extracted a lot more. It puts Cook's innings in context, the fight, doggedness and technique. Take nothing away from England, but technically and mentally no-one seems to be able to bat under pressure.

And take a look at the last of those wickets - Maharaj caught at first slip.