The appearance of the convicted Lockerbie bomber on Libyan television confirmed that a "great mistake" was made in releasing him from jail, Foreign Secretary William Hague has said.
Mr Hague said Abdelbaset al-Megrahi's release from a Scottish prison almost two years ago on compassionate grounds was "absolutely the wrong thing to do".
In footage seen by the BBC, a television presenter introduced Megrahi at what appeared to be a pro-government rally, and said his conviction was the result of a "conspiracy".
Megrahi served nearly eight years of a 27-year sentence after being convicted of killing 270 people in the bombing of Pan Am Flight 103 four days before Christmas in 1988.
He returned to Libya in August 2009 after being diagnosed with advanced prostate cancer. The Scottish Government accepted advice that he had about three months to live.
At a press conference in central London, Mr Hague said the footage demonstrated that this advice was "pretty much worthless".
He said: "I think the appearance of Mr al-Megrahi on our television screens is a further reminder that a great mistake was made when he was released. The Prime Minister and I, when we were in opposition, both strongly disagreed with that position by Scottish ministers.
"We disagreed with what has subsequently been revealed about the facilitation by the previous Labour government at Westminster of moves towards the release of al-Megrahi."
He added: "This was absolutely the wrong thing to do. It shows the medical advice it was based on was pretty much worthless and I think many people, particularly the families of those killed at Lockerbie, I think their anger and outrage at this release will be further intensified by what we have seen."
A Scottish Government spokesman said they were satisfied that Holyrood's Justice Committee has "examined all relevant aspects" of Megrahi's release. However, the same committee will shortly decide whether to call for a public inquiry into his conviction.