There have also been recriminations within the Coalition as Liberal Democrats - understood to have been backed by some Tory ministers - accused Theresa May, the Home Secretary, of mishandling the issue.
Clegg told the BBC that the most contentious parts of the legislation would be published in draft form to enable "proper scrutiny and examination and stress-testing". He said the Government would "consult and think whether existing powers are sufficient".
His comments came just hours after May made a passionate defence of the proposed measures - which the intelligence services originally wanted in place by the northern summer - as essential for tracking down criminals, paedophiles and terrorists.
The planned bill would also allow GCHQ to obtain information "on demand" and in "real time" without a warrant, and require internet companies to install hardware tracking telephone and website traffic.
In their letter, the Liberal Democrat MPs make it clear that Clegg will have a rebellion on his hands if the Government allows a major expansion of surveillance.
Prime Minister David Cameron also sought to lower the temperature among his backbenchers, insisting he was opposed to creating a "snoopers' charter".
He said: "This is not about extending the reach of the state into people's data; it's about trying to keep up with modern technology."
- Independent