Ryanair has changed its family seating policy, after Britain’s competition watchdog launched an investigation into the airline’s charges for parents to sit with their children.

Europe’s largest airline said that as of Thursday, adults would be offered “free of charge” seats next to their children after they have checked in for their flight – but at the rear of the plane. All children on the booking will be allocated seats alongside them for no fee.

Ryanair said it was a “minor policy tweak”, two weeks after it angrily described the Competition and Markets Authority (CMA) investigation as “bogus”.

“Families opting for this random allocation of seats beside each other are likely to be seated towards the rear of the aircraft cabin, as front rows tend to be reserved and sell out first,” the carrier said. It added that families who prefer to pick their seats at the time of booking and secure front row seats can still do so by paying a seat reservation fee.

Until now, Ryanair required parents travelling with children aged between two and 11 to pay to reserve what it referred to as a mandatory family seat, while up to four children can sit alongside them without a charge.

This prompted the CMA to open an investigation to determine whether Ryanair’s policy at the time was “in line with consumer law”. It found that the fee for a mandatory family seat was typically about £8 each way.

The CMA also said it believed that Ryanair was the only large airline flying out of the UK to impose this charge. Ryanair said the change would not have an impact on its revenues.

Ryanair’s chief executive, Michael O’Leary, accused the watchdog of “turning a blind eye” to the “high fares” charged by airlines on routes with no competition from the Dublin-based carrier.

He said: “The CMA has now targeted our family seating policy which has been universally embraced by consumers as the most progressive and transparent in Europe.

“Instead of promoting competitiveness and lower fares for consumers, the CMA is on a mission to force Ryanair to adopt the less transparent and less consumer-friendly family seating policy applied by most other airlines – just because it’s the industry standard.

“We will reluctantly adjust to this industry standard as we don’t want to waste time explaining to misguided regulators how badly they misunderstand what is in the best interest of UK and Europe’s consumers.

“Under our revised family seating policy, families may have to wait until after they have checked in to find out their seat allocation and are more likely to be seated at the rear of the cabin but at least the CMA will be able to claim they have done something for consumers, but sadly most consumers won’t notice.”