Q: So why the opposition?

A: The Tories and Lib Dems say they too want the terror bill in force by Christmas but worry the bill goes wider than just tackling terrorism.

They accuse the government of trying to rush through other bits of law that are not emergency measures.

Concerns have been raised that parts of the bill amount to an unacceptable infringement of civil liberties and historic rights such as habeas corpus.

The plans for detention without trial have especially provoked fears and the peers want terror suspects to be able to have their cases reviewed by a panel of judges.

The religious hatred clause should be removed from the bill, they say, and tighter rules are needed on how public bodies like customs are allowed to pass details to the security agencies.

The peers are also pressing for the scope of the measures allowing communication companies to keep data to be further restricted.

Q: Do the Lords' changes put them on collision course with the government?

A: Yes. The government used its huge majority to overturn the series of Lords' defeats when the bill returned to the Commons on Wednesday.

But peers are expected to renew their opposition to the controversial plans when the bill goes back to the Lords on Thursday.

Q: What does the government say to its critics?

Ministers have accused "unelected" peers of trying to "disembowel" what are measured and proportionate plans to tackle the real terror threat faced by the UK.

The government says it has already made concessions but will not allow the bill to be "gutted".

It points also to safeguards within the bill, such as using the Special Immigration Appeals Commission (SIAC) to review cases of detention without trial.

Q: What happens if the Lords continue to insist on their changes?

We are now seeing a game of parliamentary ping-pong, where the bill will keep passing between the two Houses of Parliament until someone gives way.

In theory, this deadlock, which could see all-night sittings of Parliament, could continue ad infinitum, especially with neither side wanting to back down.

Opposition parties do say they want to reach a consensus and they could offer alternatives to the changes they have already made, especially if they can reach a compromise with the government.

Q: Surely the government can force the new laws through the House of Lords?

The only way to do that would be to use the Parliament Act - but that could not be done until next year, meaning the bill would not become law until 2003.