Campaigner demands Burnham apology

Ms Chakrabarti, director of Liberty, demanded an apology and threatened legal action if the Culture Secretary continued "down the path of innuendo and attempted character assassination".

Her comments came after Mr Burnham suggested she had been "seduced" by the former shadow home secretary's opposition to 42-day pre-charge detention and that they had taken part in late night "heart-melting" phone calls.

Ms Chakrabarti, who disclosed last week she had tried to persuade Mr Davis not to resign his seat over civil liberties, wrote to Mr Burnham accusing him of "debasing" his office.

The Culture Secretary's aides insisted he had not intended the interpretation that had been put on his remarks, but that he regretted any personal offence caused.

The row erupted after Mr Burnham told Progress magazine he was dismayed by people who were "seduced" by Mr Davis's claim to liberal credentials.

He went on to say he found something "very curious in the man who was - and still is I believe - an exponent of capital punishment, having late-night, hand-wringing, heart-melting phone calls with Shami Chakrabarti".

Mr Davis, who is fighting a by-election on the issue of civil liberties after resigning in protest over 42 days, attacked Mr Burnham last night for indulging in "personal smears" and "lies".

In a strongly-worded letter to the Culture Secretary, Ms Chakrabarti said: "I must say that I find this behaviour curious, coming as it does from a Cabinet Minister; let alone someone with a partner and family of his own.

"By your comments you debase not only a great office of State but the vital debate about fundamental rights and freedoms in this country. Indeed you seem reluctant to engage in that debate except in this tawdry fashion. I look forward to your written apology as I'm sure does Mrs Davis."