As MI5 says threat from Isis is growing, our ability to debate it is being suppressed

The head of MI5 has warned that Isis has attempted six "mass casualty" terror attacks in the past year and will continue to plan more.

Andrew Parker, the Director General of the Security Service, has claimed that the threat to Britain is now higher than at any point in his 32-year career.

It may not yet have reached the high water mark and, despite the successes we have had, we can never be confident of stopping everything.

We are seeing plots against the UK directed by terrorists in Syria; enabled through contacts with terrorists in Syria; and inspired online by [Isis'] sophisticated exploitation of technology.

• Andrew Parker

Mr Parker added:

We need the tools to access terrorists' communications online just as much as we intercepted written communications and telephone calls in years gone by.

Separately, police have been criticised after using powers under the Terrorism Act to seize the laptop of BBC Newsnight journalist Secunder Kermani (pictured) - as disclosed by the Independent on Thursday morning.

Officers obtained an order from a judge that was served on the BBC and the journalist who has produced a series of reports on British-born jihadis since joining the show last year.

BBC colleagues, other journalists and alarmed freedom of speech campaigners have expressed their shock at the news.

Newsnight editor Ian Katz said:

While we would not seek to obstruct any police investigation we are concerned that the use of the Terrorism Act to obtain communication between journalists and sources will make it very difficult for reporters to cover this issue of critical public interest.

Jo Glanville, director of press freedom campaign group English PEN, told the Independent the current “hysteria” around terrorism was greater than in the aftermath of the 9-11 and 7-7 attacks.

If journalists go near something to do with terrorism the police can use the Terrorism Act [2000] to go after their sources.

• Jo Glanville

The media lawyer Gavin Millar, QC, also warned last month that the debate around why young Britons are going to fight for jihadi groups "has not been advanced by informed coverage because the media is in fear of the Terrorism Act".

More: This man is questioning Britain's double-standard of who it labels a terrorist