England will make an official complaint over a controversial umpiring decision on the second day of the fourth Test against South Africa in Johannesburg.

Third umpire Daryl Harper allegedly failed to turn up the speaker volume when England referred a caught behind appeal against Graeme Smith.

A noise was clearly audible on replays but Harper said he could not hear it.

"It was a crucial time, Graeme was only on 15, they had 36 on the board," said England coach Andy Flower.

Smith went on to make 105 as South Africa closed on 215-2, a lead of 35 in a match they have to win to level series and retain the Basil D'Oliveira trophy.

Having been dismissed for 180 after choosing to bat first, England were desperate for an early breakthrough, with Smith - who hit 183 in the second innings of the third Test - a prize scalp.

And they were confident they had their man when the South African skipper appeared to edge a wide delivery outside off stump from Ryan Sidebottom into the gloves of Matt Prior in the fourth over of the morning session.

The wicketkeeper, slips cordon and the bowler all appealed in unison, but on-field umpire Tony Hill remained unmoved, prompting England to refer the decision to Harper.

Although a noise was clearly heard on television replays, the Australian official said he could not hear anything decisive and concurred with Hills's original not out decision, sparking dismay among England's players.

"He's obviously hit it because you can hear the nick on the replays," said Flower.

"I don't blame him (Smith) at all for standing his ground but certainly, with the technology available, I found it very surprising it was given not out."

Following the incident, an official investigation was conducted in conjunction with Sri Lankan match referee Roshan Mahanama, when it was discovered that Harper had his speaker turned up to level four out of 10.

"We had a couple of meetings with the match referee to clarify what went on because it was at a very important stage of the game when this took place," said Flower.

"At first he claimed the audio feed was different to Sky and SuperSport (channels providing live pictures). On a subsequent investigation we found that was not the case.

"I asked him (Mahanama) again and he explained that Daryl Harper had not deemed it necessary to turn the volume up on his microphone, which I find very strange when he's trying to listen for a nick."

Technological advances such as 'Snickometer' and 'hot spot', which are much more effective at breaking down caught behind decisions, are not in use for the series because host broadcaster SABC deemed the tools too expensive.

The first day of the crucial final Test was mired in controversy when opener Alastair Cook was given out lbw following a referral to a Morne Morkel delivery which England believed should have been called a no-ball.

"We didn't make a big issue about that, we thought we would bite our lips and get on with the game," added Flower. "But this incident is a step too far."

Although Smith confessed there was a noise, he stopped short of admitting he had edged the ball.

"There definitely was a noise but I didn't feel I touched the ball," he said.

"Maybe I did, maybe I didn't, but at the time I didn't feel that I did. I thought it was my thumb on the handle.

"It's not my job to discuss what the third umpire heard. We all knew what technology was available in this series, it was explained to use by (ICC general manager) Dave Richardson before the series started, so to be crying over spilt milk now is not right.

BBC SPORT