Gambling companies are among the heaviest advertisers on radio during “school run” hours when millions of children are in the car, according to research that prompted warnings about their exposure to promotions for the national lottery, online casinos and sports betting.

Data shows gambling came second in a list of industries that spend the most to appear on commercial radio between 7am and 8am and from 3pm to 4pm, according to an analysis for the Guardian by market analysis firm Nielsen.

The analysts found that gambling accounted for 5% of all spending during school-run hours, with about 1,200 hours of ads airing during those times over the past 12 months.

The amount spent on gambling ads was exceeded only by government communications – including Covid-19 messages – and motor supplies. Nielsen does not disclose the actual spending figures because it is commercially sensitive data.

Many of the adverts are for the national lottery, but ads broadcast during the school run also include spots for betting and online slot machine brands such as Gala Casino.

After it was contacted by the Guardian, Entain, which owns Gala Casino, is understood to have added a stipulation to its media-buying arrangements to prevent broadcast during weekday school-run times.

Government statistics suggest millions of children are likely to be in the car during the period. There are 8.9 million schoolchildren in the country and the last in-depth survey by the Department for Transport survey found that 46% of children aged 5-10, and 23% of those aged 11-16, go to school by car.

Addiction experts and campaigners said the figures underscore the need for an ongoing government review of gambling regulation to take a tough stance on advertising.

Heather Wardle, Lord Kelvin Adam Smith reader in social sciences at Glasgow University, said: “Commercial gambling is rightly considered an adult-only activity, yet the way it’s advertised across radio and other media makes it very difficult to protect our children from being exposed to this.

“Evidence from the Gambling Commission shows that 7% of children exposed to gambling advertising said that seeing or hearing advertising prompts them to gamble when they were not planning on doing so.”

Labour MP Carolyn Harris, who chairs a cross-party group examining gambling harms, called for reform of “national disgrace” advertising rules. “Until we completely overhaul their access to advertising platforms, we will continue to expose children and vulnerable adults to this unrelenting attack,” she said.

The government is due to publish proposals for the reform of gambling regulation early next year.

A spokesperson for the Betting and Gaming Council (BGC) said: “BGC members abide by the strict rules set down by the Advertising Standards Authority. Indeed, since the BGC began two years ago, we have introduced a number of measures to go even further than the requirements of the advertising codes developed by both the ASA and the Committees of Advertising Practice.

“In addition, our members also ensure that 20% of their TV and radio ads are safer gambling messages.”

A spokesperson for the national lottery operator, Camelot, said it needed to advertise at all times of the day to reach as many people as possible. “We’ve always followed strict guidelines to ensure our ads don’t appeal to children, and this has contributed to it being widely recognised that the inherent risk of unhealthy play associated with national lottery games is extremely low,” said the spokesperson.