The government says more time is needed to foil complex plots
Extending the pre-charge detention limit for terrorism suspects to 42 days is "wholly unnecessary", a cross-party group of MPs and peers has said.
The Joint Select Committee on Human Rights has proposed a series of reforms which it says are a viable alternative to increasing the current 28-day limit.
They include ending the ban on granting bail in terror cases, and allowing post-charge questioning of suspects.
MPs are expected to vote on reforms to the Counter Terrorism Bill next month.
The Joint Select Committee on Human Rights (JCHR) says "no clear evidence" has emerged of any likely need to extend the pre-charge detention period.
And it describes the proposed safeguard against wrongful detention - a parliamentary vote after the 42-day power has been triggered - as "virtually meaningless".
The JCHR says the government has largely ignored the proposals it has put forward in a previous report.
Andrew Dismore, the committee's Labour chairman, said: "We are astonished - and extremely disappointed - that the government have failed even to consider our proposed alternative, in the meagre four paragraphs of official response we have received so far."
He said the alternative package would better protect the public and comply with human rights principles, "whilst also reducing the risk of alienating minority communities".
One of the JCHR's key proposals is the introduction of post-charge questioning.
Currently, once charged, a suspect accused of any crime cannot be interviewed further by police.
The JCHR wants to change this for terror cases, so that if new evidence comes to light- for example, from analysis of a computer - the suspect can be questioned about it.
The committee also wants the government to consider allowing bail to be granted, with conditions, in terror cases.
Under the Terrorism Act 2000, bail cannot be given to any terror suspect prior to charge, but the JCHR says there is a "compelling case" for making bail an option in some instances.
It says it "would enable the police to continue their investigation of those suspected of terrorism offences who do not pose a risk to public safety or a flight risk".
Another suggestion by the committee is to improve the incentives to those "on the periphery of terrorism offences" to give evidence, such as by giving better witness protection.
The committee also claims there are existing policies in place which undermine arguments for a greater detention limit.
Key among them is the option to charge someone with a terrorist offence on the basis of a lower evidence threshold than for other crimes.
The committee is holding a conference on counter-terrorism in London on Wednesday.
Under current proposals, the home secretary could immediately extend the limit on pre-charge detention from 28 to 42 days, if supported by a chief constable and the director of public prosecutions.
MPs and the House of Lords would then vote to approve it within 30 days. If they rejected it, the extension would end at midnight on the day of the debate.
Attempts to extend it to 90 days in 2005 ended in Tony Blair's first Commons defeat as prime minister.