Liberal Democrat leader Nick Clegg said it was a "sad day" for traditional British liberties after plans to extend the pre-charge detention of terrorist suspects to 42 days was passed in the House of Commons.
The Counter-Terrorism Bill was passed by 315 votes to 306 - a Government majority of just nine.
Mr Brown was effectively saved by the votes of the nine Democratic Unionist MPs who at the last minute agreed to march into the division lobbies with the Government.
Mr Clegg said: "What we have seen is the sacrifice of principle in order to save the skin of a sinking Prime Minister. It has nothing to do with the substance of the matter," he told Sky News.
"It also appears to me at least to have been the victory of pork barrel politics over principle as well."
Shadow home secretary David Davis said the Government had won the vote but lost the argument.
"It wasn't the argument that won the day, it was the whips operation. Gordon Brown can't be proud today," he told Sky News.
He said that the nine DUP MPs who saved the Government from defeat looked "very uncomfortable" in the chamber of the House of Commons.
Shami Chakrabarti, the director of civil liberties group Liberty, said: "Whilst disappointed, Liberty pays tribute to the brave parliamentarians of all stripes who held their nerve against the pressures of party politics and the terrorists' attempts to provoke us to abandon our values.
"Recent years have shown how forgetting Britain's moral compass has left our country less safe. So, on to the House of Lords - once more the guardian of fundamental rights."
