The news that there are "significant numbers" of Britons fighting for extremist Islamist groups abroad, one of whom is implicated in the murder of US journalist James Foley, has prompted calls for action against radical Islamism in the UK.

Speaking on BBC Breakfast, Foreign Secretary Philip Hammond said that the government was aware of 'significant numbers' of Britons fighting for Islamist organisations abroad. "That's one of the reasons why this organisation represents such a direct threat to the UK's national security.

"Many of these people may seek at some point to return to the UK and they would then pose a direct threat to our domestic security."

Christians from across the political spectrum are calling for action regarding jihadism present in the UK; from better border controls to sharing the love of the gospel.

"Part of the challenge seems to be that disaffected young men are looking for a sense of purpose to give their lives to," said Dr Krish Kandiah from the Evangelical Alliance. "As churches we should be offering these young men a vision of what it means to live for God showing his love and compassion in the world. A lot of these young men feel a sense of injustice about the state of the world and then get captured by this destructive ideology.

"The good news of Jesus should offer them a better hope and vision of what the world could look like and to help change it through mercy and peace."

There are calls for justice to be brought to any militants who return home. "Murder is murder, war crimes are war crimes, and if any have been involved in them they will get the full force of the British justice system," said Colin Bloom from the Conservative Christian Fellowship. "It's unlikely they would want to come back here and lead a quiet life - they would want to create trouble and strife. But I think very few will come back. They will probably end up losing their lives in Iraq, they're engaged in a very bloody war where casualties are high on both sides.

"We need to get on our knees and seek the Lord, and cry out to him for what is happening. And secondly we need to urge our MPs for an unambiguous response to what is happening in Iraq, especially in the light of this James Foley beheading."

Dr Jenny Taylor, the founder of Lapido Media and an expert on Islamism, said that there have been warnings about extremist jihadists since the 1990s. "There are aspects of Islam that are supremacist and predatory and implacable, there is a fear dimension that has never been taken seriously. It's been dismissed as Islamophobia and rubbish, and voices from the street have been silenced.

"We have to do everything in our power to warn and take appropriate steps to stop jihadists getting back into the country, stop them at the border, we have to understand more about who is building our mosques, and we have to get real... I do believe ISIS has to be stopped, because I do believe it could not be more serious, what is facing us could not be more serious and I still think we haven't reckoned with it."

Andy Flannagan, who runs Christians on the Left, called for prayer for both the victims of the violence and the perpetrators. "Both in the short-term and the long-term what is needed more than anything is a change of heart in those who have been ensnared by twisted ideology. Force may be required to protect the innocent, but that change of heart is unlikely to happen at the point of gun.

"Sadly the situations now making the headlines are only the tip of an iceberg that we as Christians on the Left have been flagging for some time. We have been working with organisations like Christian Solidarity Worldwide and Open Doors in an attempt to move religious persecution further up the agenda of the Government and the Opposition. It is painful that it has taken circumstances as tragic as these to make people aware of the scale of the problem."