Alan Johnston, the BBC correspondent abducted by Islamic extremists nearly four months ago, has been released by his kidnappers in Gaza early Wednesday morning.

Johnston, 45, was seen leaving a City building accompanied by armed men. He described his experience in captivity as "appalling" but said it was "fantastic" to be free.

The Archbishop of York, Dr John Sentamu, said, "Hallelujah!" when he heard the news of Johnston's release. He has held regular prayer vigils for the BBC correspondent since his kidnap and also appealed for his release on al-Jazeera.

Johnston was unable to see sunlight for more than three months and was even chained up for a 24-hour period.

A worldwide campaign has been led by media and political leaders since his abduction, condemning the abduction. More than 200,000 people signed up to an online petition calling for his release.

Johnston was received by Hamas officials early on Wednesday morning, and was later taken to appear alongside Hamas leader Ismail Haniya.

The BBC correspondent, obviously thrilled with his release, expressed his gratitude to all those who had worked and campaigned for his freedom.

His release follows recent threats from Hamas' military saying it was actively working towards ensuring Johnston's release, and even warning the abductors that it was willing to use force if necessary.

Johnston was abducted on 12 March by a group called the Army of Islam. Since then, the militant group has released three videos - two of which showed Johnston - saying that it would kill the correspondent if its demands for the release of Muslim prisoners in British custody were not met.

It was also reported this morning by a senior Hamas official, Mahmoud Zahar, that no deal was done with the kidnappers to secure the release. He denied that Hamas had worked so ferociously towards securing Johnston's release to "receive favours from the British Government".

Zahar said: "We did this because of humanitarian concern, and to achieve a government aim to extend security to all without fear."

Johnston later appeared in a press conference alongside Hamas leader Haniya, where he thanked those who had supported his release. He added that his captivity had been "occasionally quite terrifying".

He said: "It became quite hard to imagine normal life again. The last 16 weeks have been the very worst of my life. I was in the hands of people who were dangerous and unpredictable.

"I literally dreamt many times of being free and always woke up back in that room."

The BBC correspondent confirmed that he was not tortured at all during his captivity, but that he did fall ill from the food given to him.

For the first month he was abducted he was able to see the sun, but after that he was moved to a dark shuttered room where he was kept until just last week. He did, however, have access to a radio, and revealed that he listened to the BBC World Service and was able to keep up to date with the efforts to free him. He said that news of global demonstrations supporting his freedom was a great comfort to him.

Johnston was told that he was not harmed physically until just half an hour before his release, when he was hit. He explained: "The kidnappers seemed very comfortable and very secure in their operation until... a few weeks ago, when Hamas took charge of the security operation here."

He added that he was looking forward to seeing his family back in Scotland and said he regretted that he had brought such turmoil to their lives over the past four months.

The BBC said it is both relieved and delighted at Johnston's release.

Johnston left the Gaza Strip later on Wednesday morning, travelling to Israel.