has just detonated a homemade device,

killing 22 people attending an Ariana Grande concert.

It was the deadliest terror attack in the UK's most deadly year since the 7/7

bombings in London in 2005.

One year on, the threat from Islamist inspired extremism

shows no signs of abating.

The terror threat level in the UK remains severe,

one step down from its highest possible level,

and security officials say it could remain this way until 2020.

In the UK alone since the Westminster attack in March last year,

with the police we've thwarted a further 12 Islamist terror plots--

12 occasions where we have good reason

to believe a terrorist attack would otherwise have taken place in our country.

MI5 and police are dealing with unprecedented numbers of leads

following last year's attacks in Manchester and London.

There are 500 separate investigations

and 3,000 subjects of interest being actively watched.

The heightened state of vigilance

is also explained by the shifting nature of the threat.

As ISIS has surrendered its strongholds in Iraq and Syria,

so the threat from returning jihadists has also grown.

At the same time, online extremists

are inspiring would-be terrorists remotely, encouraging and guiding

them to carry out low tech, lone wolf attacks which are so difficult to detect.

In this climate,

dropping your guard is not an option for the security services and the police.

We are highly effective at preventing attacks in this country,

but highly volatile people

who are intent on doing something absolutely terrible,

and in that act are quite happy, maybe even pleased, to kill themselves.

And to use low tech methods,

these are difficult things to defend against.

For a city which prides itself on its diversity,

the events of last year are still a shock.

But for the UK as a whole there is no sign

that the wider threat will ease anytime soon.