No deal has been done with Libya over the transfer of the Lockerbie bomber, Justice Secretary Jack Straw insisted.
And he added it would be for Scottish ministers to decide if Abdelbaset Ali Mohmed Al Megrahi is returned to his home country.
Al Megrahi is currently serving a life sentence in a Scottish prison after being convicted of bombing Pan Am Flight 103 over Lockerbie on December 21 1988.
Scotland's First Minister Alex Salmond restated the Scottish Government's opposition to any deal which could see him returned to Libya earlier this month.
But in a letter in The Herald newspaper, Mr Straw said: "No deal has been done with Libya for the transfer of Al Megrahi."
He added: "The decision on whether or not a prisoner detained in a Scottish prison is transferred to another country is a matter for Scottish ministers, not the United Kingdom Government. From the outset we have been clear with the Scottish Executive about this fact and have not at any time sought to undermine due process in Scotland."
Scottish justice secretary Kenny MacAskill accused the UK Government of going back on assurances that Al Megrahi would not be included in a prisoner transfer deal with Libya.
Mr MacAskill said the Scottish Government was previously told that Al Megrahi would be excluded from an agreement between the UK and Libya on the transfer of prisoners. But he claimed Westminster's position had now changed, and the Scottish Government was being "undermined".
Mr MacAskill claimed that if Al Megrahi was not specifically excluded from a deal on prisoner transfer, any decision by the Scottish Government could be challenged in the courts by judicial review.
Speaking on BBC Radio Scotland, Mr MacAskill said: "That is why we sought the assurance that Mr Al Megrahi would be specifically excluded."
