Theresa May’s government has been accused of changing the rules on public appointments to make it easier in future for ministers to pick their political allies for senior jobs at the BBC and regulators such as Ofsted.

The new code on public appointments will give ministers greater powers over who oversees a raft of agencies, watchdogs and advisory committees, while weakening the involvement of the independent commissioner for public appointments, who scrutinises the system.

Labour said the changes, which will come into force on 1 January, represent a “power grab” by ministers and risk returning to the days of patronage and cronyism in public life.

Ministers have always had the final say over appointments to senior public sector jobs, advised by a panel that shortlists “appointable” people. However, independent assessors, chosen by the commissioner to oversee the most important competitions, will be abolished in favour of independent senior panel members picked by ministers.

The members will have to be independent of the departments and not currently politically active, but the commissioner will only have a consultative role.

Ministers will also be able to overrule the panel by choosing candidates not deemed to be appointable and have the right to dispense with an open competition without the permission of the commissioner, although they will have to consult with the watchdog and openly justify the decision.

Competitions under way, including searches for a chair of the BBC board and chair of Ofsted, will continue to be regulated under the old regime, but it will apply to future competitions run for those posts and many others.

The government argues that the decision increases the accountability of ministers, but Labour’s Andrew Gwynne warned about the greater risk of them “appointing chums and donors to public office”.

“This Tory power grab is divisive and a worrying undermining of the role of the independent commissioner for public appointments,” he said.

The code was welcomed by Peter Riddell, the commissioner for public appointments, as an improvement on previous proposals set out by Sir Gerry Grimstone, a businessman who conducted a review for the government.

However, he warned in his annual report last autumn that he intended to highlight any abuses if ministers did not interpret the code in the spirit of making public appointments on merit.

In a statement about the code, Riddell said: “I have had constructive discussions with ministers and officials as they have developed the code over the past few months. They have not accepted every suggestion, but they have made a number of important changes, notably to reinsert fairness in the list of guiding principles and the commitment to consult me both about the appointment of senior independent panel members to assessment panels and about cases where exemptions are sought from holding competitions to make appointments.

“I believe that the real test for the new arrangements will be how they are interpreted by ministers. To preserve the balance between their right to be fully involved in the process and to take the key decisions, while ensuring that appointments are made on the basis of merit, with candidates being judged on a fair and equal basis.”

Asked about Labour’s criticism, Chris Skidmore, the minister for the constitution, defended the new code, saying it “rightly places ministers at the heart of the appointments process, given their accountability to parliament for public bodies”.

“The new code introduces greater transparency into the system and reiterates the role of a strong, independent regulator of the process through the commissioner for public appointments. I want to see a process that champions diversity and builds a democracy that works for everyone,” he said.

The proposals had been criticised in their consultation stage by the former commissioner for public appointments Sir David Normington and the parliamentary committee on standards in public life.

Before the publication of the new code, he warned that 20 years of progress on improving the public appointments process could be put at risk.

In July, the standards committee said: “The committee fears that the changes will remove some of the independent checks and balances of the public appointments process and may have the unintended effect of offering limited protection for ministers who wish to demonstrate they have appointed on merit alone.”

Since the original proposal, the code has been slightly altered to say the commissioner must be consulted about exemptions and the appointment of senior independent panel members, but the essence of the change remains.

It comes after a number of cases in recent years in which ministers have been criticised for appointing allies to senior public positions.

Under David Cameron, Philip Dilley, an engineering chief and former business adviser to the prime minister, was given the job of chair of the Environment Agency and David Prior, a former Tory MP and now minister, was appointed as chairman of the Care Quality Commission. There were also criticisms of some of Cameron’s appointments he made on his departure from No 10.

Last night, Lord Bew, chair of the committee on standards, told the Telegraph that the idea of putting political appointees through an interview process should be considered.

He said his committee was “very interested” in tightening up procedures for so that those entering the House of Lords have to go through a more rigorous tests of suitability.