Walking round Brussels is like walking round a city on Christmas Day

Walking round Brussels today is a bit like walking round a city on Christmas Day.

Pretty much everything is shut, a few tourists and some cafes or bars doing a lively trade because there's nothing else to do.

It's a touch surreal and easy to forget what's behind this lockdown - a terror threat based, we're told, on precise, specific intelligence suggesting a serious and imminent risk of attack.

The decision to shut down a city is not taken lightly.

It's socially and economically damaging and offers a goal of sorts to those seeking to damage society.

The Belgians know they need to get this place working again but the time they are taking is a clear indication of their concern.

In the past 24 hours, 21 people have been arrested and 26 raids completed.

But there remains no sign of the man at the centre of this search - Salah Abdeslam is still on the run.

He is at the heart of this alert but it is now on a scale which suggests intelligence based on more than just his presence.