A London preacher has claimed that he and a suspected British jihadist in the Islamic State went to church together.

The Telegraph had previously reported that preacher Daniel Downer of Walthamstow may hold important information on Nero Saraiva, whom security services believe is a companion of Jihadi John, after he was mentioned in a post in Saraiva's Twitter account.

Jihadi John is the unnamed Islamic State fighter with a British accent, who is featured in many of the execution videos published by the ISIS.

The Telegraph later interviewed Mr Downer, who revealed that he met Saraiva at a gym in Walthamstow in 2007, and subsequently invited him to church.

"He attended church with me on a few occasions and then I did not hear from him again," the preacher told the Telegraph. He also said he was only aware of Saraiva's jihadist activities when he was approached by journalists after Saraiva's tweet.

Saraiva gained the attention of the authorities after he posted advanced notice of an upcoming ISIS video in this Twitter account.

"Message to America," the tweet said. "[T]he Islamic state is making a new movie. Thank [you] for the actors."

The "movie" is apparently the execution video of American journalist James Foley, which was released 40 days after Saraiva's post.

Eleven days later, Saraiva tagged Mr Downer's Twitter account in a post asking: "Do [you] have any pictures of my son?" He also sent Mr Downer a tweet with a picture of himself in what seemed like an Islamic country doing the single finger salute associated with the Islamic State.

Mr Downer expressed puzzlement at why Saraiva would send him that tweet. "I don't understand why he would think I have pictures of his son," the preacher said.

Saraiva, a Portuguese national who had lived in Angola, is believed to have come to Britain in 2003 but may have left for Syria after converting to Islam in 2012.