Fears are emerging over the complexity of the government’s new welfare system after data revealed that one in five applicants is being turned down because they are failing to comply with the application process.

Ministers have already been forced to slow down the rollout of universal credit and to ensure that claimants receive their payments sooner after concerns that some were waiting well over a month for funds and were facing mounting rent arrears. Some welfare campaigners now fear that the complexity of the application system has left thousands of applicants falling foul of the rules.

According to data released under the Freedom of Information Act, which analysed applications for universal credit over one month, a fifth were turned down because of “non-compliance with the process”. Of those, half failed to book an initial interview. The rules state that if the applicant has not called a helpline to set up an interview within a week of making their application, their claim may be closed.

A total of 6% of all applications were ended because applicants failed to sign a “claimant commitment” setting out the conditions of their payment. A further 4% had their application closed for failing to attend an interview at a jobcentre.

With around 100,000 new claims for universal credit each month, this could mean that tens of thousands of people will not receive a payment.

Frank Field, the Labour chair of the work and pensions select committee, said that the complexity of the system was a “mega issue” and his committee would be investigating. “I have tried to enrol myself [for universal credit] and failed,” he said. “I wonder if the ministerial team have tried.”

A spokesman for the Department for Work and Pensions said the figures “don’t capture the reasons” for people not completing their application. “It may be they’ve found higher-paying employment and no longer need support,” he said. “Almost 800,000 people have already applied for universal credit successfully, and anyone struggling with the process can call the helpline or visit their local jobcentre, where staff will help them.”