The family of a cyber terrorist are "delighted" that he has reportedly slipped back into Britain after being released from prison in America.

Babar Ahmad was jailed for 12-and-a-half years in the United States for helping support terrorist groups online.

He reportedly returned to the UK in secret last week and is said to have celebrated the Muslim festival Eid with his family in south London.

"We, the family of Babar Ahmad, are delighted to announce that by the grace of God Babar has returned home to us after 11 years in prison," his relatives said in a statement.

"Our lives will be enriched by his return."

The family described the last 11 years as "indescribably difficult", and added that they were "heartened" by US judge Janet Hall's sentencing comments that Babar is a "good person" and unlikely to re-offend.

Babar, 41, spent 10 years behind bars in the UK before losing a protracted battle against extradition to the US.

He was sentenced in July last year after pleading guilty to setting up a group of pro-jihadi websites to raise money, recruit fighters and get supplies for the Taliban and other terror groups.

"Eleven years of solitary confinement and isolation in 10 different prisons has been an experience too profound to sum up in a few words here and now," Babar said in a statement.

"In October 2012, I was blindfolded, shackled and forcibly stripped naked when I was extradited to the US.

"Last week, US and UK government officials treated me with courtesy and respect during my journey home. Today, I have absolutely nothing. Yet I am rich. All praise be to God.

"In time I look forward to sharing reflections on my experience to help inform others.

"I recognise that the world has moved on since 2004, yet in some ways sadly it has failed to progress.

"For now, I intend to reconnect privately with my incredible family, to whom I owe so much. It was a great joy to celebrate Eid with them for the first time in 11 years and to hug three of my nieces and nephews whom I had never met before. It has been a long time."

It has been reported that the counter-terrorism command at Scotland Yard is considering measures to monitor Babar.

A spokesman for the Met Police said: "With regard to whether we are looking at someone or measures, we would never discuss that."

Ahmad was released on June 19 and is "entitled to return to the UK", according to the Home Office.

"Babar Ahmad was extradited to the US on October 5, 2012 for trial on terrorism offences," a spokesman said.

"He subsequently pleaded guilty to conspiracy and providing material to support terrorism and was sentenced to 12-and-a-half years' imprisonment.

"Ahmad had used every opportunity, over eight years, to frustrate and delay the extradition process but he finally faced justice and was put behind bars.

"The sentence he was given by the US courts concluded on June 19.

"As a UK citizen, Ahmad is entitled to return to the UK."