The figure was revealed as it emerged independent inquiries into alleged collusion by the security forces into three murders in Northern Ireland is almost £69m.

The government bill also includes inquiries into the deaths of loyalist leader Billy Wright and Portadown man Robert Hamill.

The news comes days after it was revealed that many of the 180 staff working for the Historical Enquiries Team, set up to investigate murders during the Troubles, could temporarily lose their jobs because the government has withdrawn £1.5m funding.

Up to the end of September, the inquiry into the murder of Mrs Nelson, which opened in April 2005, has cost almost £32m and could last for another 18 months.

She was killed in a loyalist booby-trap car bomb attack outside her home in Lurgan, County Armagh, on 15 March 1999.

The murder was claimed by loyalist splinter group, the Red Hand Defenders, but there have been allegations of security force collusion because of Mrs Nelson's role as solicitor for the nationalist Garvaghy Road Residents' Coalition and other high profile cases.

The inquiry into the killing of Loyalist Volunteer Force leader Billy Wright, which opened three years ago, has cost almost £19.5m and is expected to last for at least another six months.

The inquiry into Robert Hamill's murder will not begin hearing evidence in public until early next year, but has already cost almost £18m.

DUP Councillor Dr Philip Weir hit out at the costs: “Inquiries into the deaths of Rosemary Nelson, Robert Hamill and Billy Wright have already cost the taxpayer in Northern Ireland £69 million. This follows on from the revelation that the Saville Inquiry into Bloody Sunday is close to passing the £200 million mark, with £27 million having been paid out since January 2005 despite no witnesses being heard over that period.

"The Nelson and Hamill Inquiries were granted as concessions to republicans at the Weston Park talks in July 2001..

"While families understandably want those responsible for their loved ones’ deaths brought to justice, these massive sums are impossible to justify. Unfortunately much of the thrust behind them appears to be politically motivated and the likelihood of them satisfying such an agenda are virtually nil.

"Furthermore these sums are being racked up within an environment where funding has been withdrawn from the Historical Enquiries Team with many officers set to lose their jobs at least temporarily. Less vocal victims understandably question why investigations into the deaths of their relatives do not receive the level of focus and resources."