WORKS needs to be done to repair the shattered relations between governments and internet firms if they are to share data to stop terrorists, according to the former head of MI6.

Speaking for the first time since he stepped down in November, Sir John Sawers said that it was essential for the two sides to agree on data-sharing to stop the terrorists.

He stressed there could be no online "no-go areas" the UK Government could not access as he launched a new study of attitudes towards bodies like the security services at an event in London.

Sir John blamed the breakdown in trust on revelations by Edward Snowden, the former American spy agency contractor who disclosed the extent of surveillance and electronic monitoring by the US and UK.

Facebook also faced criticism in the wake of the jailing of two men for the murder of Fusilier Lee Rigby, after it emerged one of his killers had talked on the site about intending to murder a soldier in public five months beforehand.

Sir John backed Prime Minister David Cameron's assertion that there cannot be "no-go areas" online or in other forms of communications.

He said: "Of course there is a dilemma here because the general public and politicians and the technology companies, to some extent, they want us to be able to monitor the activities of terrorists and other evil doers but they do not want their own activities to be open to any such monitoring.

"I think one benefit of the last 18 months' debate is that people now understand that is simply not possible and there has to be some form of ability to cover communications that are made through modern technology.

"The Prime Minister must have been right when he was saying last week that you cannot afford to have complete no-go areas, we cannot have no-go areas in our communities where the police cannot go, because that just allows space room for the evil doers to ply their trades.

"It is the same in the virtual world.

He added: "If you allow areas which are completely impenetrable, then, okay, you might feel comfortable that your communications are private and no one else can see them, but so are those who are trying to do you down and undermine your society."