Online gambling companies have agreed in principle to a voluntary “whistle-to-whistle” ban on advertising during live sports, in an effort to address concerns about their impact on children.

Companies such as Bet365, William Hill and Ladbrokes would agree not to advertise during live sports, including after 9pm if the event started before the watershed.

While the proposals have yet to be approved, they are likely to be rubber-stamped at a meeting of the five major gambling industry associations next week, with a view to implementing the ban within six months.

A senior gambling industry figure said he would be “surprised and disappointed” if the measures were not agreed and said that while not every online betting firm would support them, all were likely to comply.

“It would be a very brave company that would stick its head above the parapet in isolation,” he said.

The whistle-to-whistle ban, which excludes horse racing, would involve the industry falling into line with Labour party proposals.

The advertising proposals, first reported by the BBC, have been put forward by the Remote Gambling Association (RGA), which represents online betting firms.

Labour’s deputy leader, Tom Watson, said: “I’m delighted that gambling operators have adopted Labour’s proposal of a whistle-to-whistle ban on gambling advertising during live sport.

“With over 430,000 problem gamblers in the country, many of them children, the number of adverts during live sports had clearly reached crisis levels.

“There was clear public support for these restrictions and I’m glad that for once the industry, led by [the RGA], has taken its responsibilities seriously and listened.”

Several chief executives in the gambling industry, including the bosses of William Hill and Paddy Power Betfair, have said they would support greater restrictions on advertising to protect children.

Concern about the normalisation of gambling has risen due to the sheer volume of ads during televised sport.

Research by the Guardian during the World Cup found that children were “bombarded” with 90 minutes of gambling adverts during the tournament.

Shares in gambling companies fell on reports of a plan that would restrict their ability to reach TV viewers, while broadcasters are also likely to take a significant hit on lost advertising revenue.

One senior executive at a media agency told the Guardian that gambling ads were worth £200m to broadcasters last year, with the majority going to Sky and, to a lesser extent, ITV.

Online gambling companies are thought to have learned a lesson from the resistance shown by the Association of British Bookmakers, which fought tooth and nail against the cut in maximum stakes on fixed-odds betting terminals.

Their campaign was ultimately unsuccessful and caused considerable damage to the industry’s reputation over efforts to prevent curbs on machines that the government branded a “social blight”.

RGA chief executive Clive Hawkswood is thought to be determined to get the measure approved by the gambling industry before he steps down in January.

It requires agreement from the National Casino Forum, Association of British Bookmakers, Bingo Association and the amusement arcade body Bacta, although their blessing is likely to be a formality as the online industry is by far the biggest TV advertiser.

The RGA has also put forward other proposals but is expected to stop short of adopting Labour’s stated policy of banning gambling companies from sponsoring football shirts.