One of the UK's largest and most respected youth organisations will no longer compel its new members to take a religious oath.

In a move that delighted the British Humanist Association (BHA), the Air Cadet Organisation, which was formed in 1938 and played a key role in the second world war, is to offer future cadets the option of a non-religious oath. The decision follows a campaign by the BHA and the United Kingdom Armed Forces Humanist Association (UKAFHA), after they had argued that the organisation needed to recognise that many of its recruits were non-believers.

The development is likely to be studied closely by other youth organisations. Both the Scout Association and Girlguiding UK are consulting on changing their pledges so that they are inclusive of young people without a specific faith.

With almost 41,000 members, aged from 13 to 20, in more than 1,000 squadrons across the UK, the Air Cadets describes itself as the world's largest youth air-training organisation. Around 40% of RAF officers and 50% of aircrew are former cadets. At present cadets can only make the religious promise, usually at a ceremony presided over by their unit's padre or commanding officer. The vow says cadets will strive "to be a good citizen and to do my duty to God and the Queen, my country and my flag". Humanist groups successfully argued that the corps must provide a non-religious oath or it would fall foul of European legislation and the Ministry of Defence's policy on equality and diversity.

"The Air Training Corps is a significant youth organisation," said David Brittain, general secretary of UKAFHA. "According to repeated surveys, 65% or more of teenagers state they are not religious, and by failing to provide a non-religious oath the organisation has excluded a significant number of young people of good conscience who do not believe in any god and are not willing to lie by saying words they don't believe."

Brittain said other cadet forces would have to follow the air cadets' example: "While we welcome this news from the ATC, there is still work to be done in ensuring that all Ministry of Defence-sponsored youth organisations provide a similar promise. To not offer an alternative to the religious promises is divisive, unfair and deeply sad."

The news was greeted with dismay by some Christian organisations. "I'd like to see everyone following Christ and taking the pledge," said a spokesman for the Soldiers' and Airmen's Scripture Readers Association. "I can't see a truly Christian organisation dropping a pledge to Christ. It's a hollow pledge if they don't believe the words they are saying. You can't tell people what to believe."

Andy Tilsley, a spokesman for ChristChurch London, said the decision raised broader questions. "Should we change the words of the national anthem because they include 'God save our gracious Queen'? What are people threatened by?"

However, the BHA's chief executive, Andrew Copson, said British society was changing dramatically and praised the cadets for recognising it. "Over two-thirds of young people have a non-religious identity and that proportion is growing all the time," Copson said.

The Scouts and Guides were granted exemptions from the Equality Act in order to allow them to continue to require their members to make a religious pledge. Humanist groups say the pledge is tantamount to a "discriminatory promise excluding non-religious young people not believing in a god".