After Ed Balls was appointed as shadow home secretary, there were some who expressed doubts over Ed Miliband's commitment to civil liberties. It was widely thought that Balls, long seen as one of the more authoritarian members of Labour's top team, would not miss an opportunity to attack the coalition as "soft on terror".

But Ball's interview with the Sunday Telegraph, his first since becoming shadow home secretary, should go some way to silencing his critics. He reveals that Labour is prepared to support coalition plans to cut the pre-charge detention period from 28 to 14 days, and suggests that the party is prepared to consider alternatives to control orders. More strikingly, he admits that Labour lost its reputation as a party which "protected liberty as well as security".

I'm less surprised than some at Balls's apparent conversion to civil liberties. It is now widely acknowledged within Labour circles that the party too often restricted liberty without advancing security. Even the former security minister Tony McNulty -- one of those responsible for much of Labour's anti-terrorism legislation -- recently called (£) for the introduction of a 14-day limit and condemned control orders as a "clumsy tool" that should be abandoned.

On a purely political level, there is also a big opportunity for Labour to embarrass the Lib Dems. On issues such as tuition fees and spending cuts, Nick Clegg was able to claim, however unconvincingly, that the state of the public finances meant he had no choice but to change course. But on civil liberties no such defence is available to him. If, as seems likely, the coalition retains control orders -- better described as a form of house arrest -- the Lib Dems will be forced to compromise on a fundamental point of principle.

But whatever the political calculations involved, we should all be grateful that for the first time since 11 September 2001, a mature debate on civil liberties now seems possible.

UPDATE: Balls was also on The Andrew Marr Show this morning, where he fleshed out his position. He reaffirmed his support for a 14-day limit but warned that the coalition was "way too" liberal on CCTV and the DNA database. So clearly he won't be joining Liberty just yet ...