Cameron says plans were approved by Tory and Lib Dem ministers but Clegg says he just agreed to study proposals

David Cameron and Nick Clegg have been involved in pointed exchanges across eight time zones over controversial government plans to monitor emails and allow judges to sit in secret in some trials.

The prime minister was first out of the blocks when he highlighted No 10's irritation with the Liberal Democrats after they raised concerns about the proposals. As he flew to Japan on a trade mission, Cameron said leading Liberal Democrat cabinet ministers had sat on the committees that approved the plans.

The deputy prime minister then hit back by authorising his spokesman to say that Clegg had simply agreed to look at the email plans. The spokesman said: "The deputy prime minister agreed at the NSC [National Security Council] that the government would look at proposals to address the police's technological gap to deal with serious criminals and terrorists.

"But he also made clear that they could only proceed if they took into account and protected civil liberties.

"The full details of those proposals have not yet been bought forward by the Home Office. When they are, they must be carefully scrutinised to get the balance between security and liberty exactly right.

"The pre-legislative scrutiny the deputy prime minister talked about last week is very much part of that process. The Liberal Democrats will continue to put the protection of civil liberties at the top of the political agenda as the Coalition Agreement makes clear."

The tetchy exchanges show how the email and secret court plans are pulling the coalition in different directions in the runup to local elections next month.

Downing Street is frustrated with Clegg after he wrote a letter to fellow ministers on the cabinet's National Security Council raising concerns about the creation of the so-called secret courts. He also invited civil liberties groups to challenge government plans to give the security services access to internet data.

Cameron, who made Clegg chairman of the cabinet's home affairs committee as part of their coalition deal, said the plans had been approved by Tory and Lib Dem ministers. "I think everyone needs to be patient. They need to see what is proposed, both in terms of this court issue and in terms of telephone calls and emails.

"Why would we be doing this in a cabinet of Conservatives, including quite a lot of liberal Conservatives, and Liberal Democrats, if there wasn't a problem? In both areas there are pressing problems we need to deal with."

Cameron spoke out following twin interventions by Clegg last week. In a letter to fellow ministers, Clegg demanded a series of safeguards before he would agree to allow the creation of special courts. Under the plans, sensitive intelligence material would only by seen by lawyers known as special advocates who could not discuss with the claimants or their lawyers what they had seen or heard in secret court sessions.

Cameron defended the plans, saying: "We have a problem in which you can have people coming and claiming money off the British state and there is absolutely no way of the state defending itself in court.

"There are some people who will never be satisfied. But I think anyone who is reasonable – who understands that national security matters, who understands that being able to present intelligence in court matters – I think they will find favour with these proposals.

"But it will be a difficult argument. These things always are. But people need to be patient and wait to see the detail. I'm confident we'll be able to deliver what is necessary."