6.00pm:UPDATE: Police confirm that a device linked to the incident has been examined and was “not a viable explosive device”.

Detective superintendent Michael Hanlon said: “We would like to reassure the public that there is no suggestion at all that this was linked in any way to terrorist activity.”

4.50pm:UPDATE: The man at the centre of today’s siege threatened staff with a bomb that he claimed was strapped to his foot, it has been reported.

One eye witness described how she attempted to walk into the bank just as terrified staff were streaming out of the front door.

She told the Watford Observer: “I was going in to do some banking and I could hear that something was happening inside. I did not see the man but I heard him shouting.

“The staff came out and told me to leave the area and call the police. They said that the man had threatened them with a bomb strapped to his foot. They were very upset by it.”

The witness, who did not wish to be named, also described the remarkable bravery of one particular bystander, who stood in front of the door to warn other shoppers of the danger inside.

She added: “He stood in front of the door to stop people coming near the bank. Others were shouting at people not to go in.”

Police sources have told the Watford Observer that no hostages were held during the incident.

4.10pm:UPDATE:

Hertfordshire Constabulary have just release the following statement following a press conference in Shady Lane, Watford... "This incident has affected hundreds of people in Watford town centre but what we have seen today is real community spirit and support from the public as we took action to respond.

"Hertfordshire Constabulary would like to put on record its thanks for the co-operation of those who have been inconvenienced by today’s unusual events which has led to the arrest of a 23-year-old man.

"The incident began with a call to our control room at around 10am. Dozens of police officers, including specialist firearms teams, were immediately sent to the scene – the Co-op Bank in Market Street.

"What unfolded over the next few hours, was a complicated and fast moving situation which came to a successful and safe resolution with a suspect agreeing to surrender. This was achieved through the assistance of bomb disposal experts from the Ministry of Defence.

"The safety of members of the public and officers has been our priority throughout the day. I would again like to thank the local business and wider community for their co-operation throughout as difficult decisions, such as the evacuation of local premises, had to be executed swiftly.

"I would also like to thank members of the media who worked with us in the first hours ensuring we could establish what was happening inside the building.

"We now move into a stage where a full investigation will be required. This will be led by Bedfordshire and Hertfordshire Major Crime Unit.

"As you can appreciate now we have a man detained in custody we are unable to make any further comment or speculation about today’s events. Please look at our website for any further updates.

4pm:UPDATE: Hertfordshire Constabulary has released further details in the wake of today’s dramtic siege. The force:

  • Said it does not yet know the nature of the explosives and are still examining what was found.
  • Confirmed that no shots were fired, saying loud bangs heard at scene came from elsewhere.
  • Announced that an investigation is being commenced by the Beds and Herts Major Crime Unit.
  • Explained that armed officers entered building after the man was led away to secure the scene.
  • Confirmed the involvement of the Explosive Ordnance Disposal Team.

2.33pm:UPDATE: Police have lifted the cordon and reopened Market Street.

2.31pm:UPDATE: Armed police have left the building and are leaving the area but the cordon is still in place.

Army bomb disposal experts have also left area. One officer is now guarding bank.

2.17pm:UPDATE: Police remain on the scene and are still preventing access to the immediate area.

Watford Observer reporter Adam Binnie, who covered much of the siege from the upstairs office of a Market Street solicitor, is among dozens of people holed up in the Mangans Pub.

He said: “There’s a large police Landrover outside and a big personnel carrier parked nearby.

“The police seem to be tidying things up now. The cordon is still in place and there is still a big group of people trying to see what’s going on.

“It all seems to be over now but the police are still inside the building. It is still unclear why armed police stormed into the building after the man had been taken out.

“People seem to have been calmed down now but we’re not being allowed to leave the pub.”

2.04pm:UPDATE:

Police statement released....

“Following a three-and-a-half hour stand-off at the Co-Op bank in Market Street in Watford today, officers from Hertfordshire Constabulary with the support of the EOD (bomb disposal) have in the last few minutes safely secured the arrest of a suspect who had been refusing to leave the bank.

“An explosive device of some kind, as yet we don’t know what this is, has been recovered. The suspect is being taken into police custody for further questioning. No members of the public have been harmed, however there was considerable disruption in the town centre.”

1.58pm:UPDATE: Police recover "explosive device" from building

1.55pm:UPDATE: About a dozen armed police storm into bank.

1.50pm:UPDATE: A man in camouflage wearing a beret, and another man dressed in black with a large rucksack have left the bank.

A police 4x4 has driven into Market Street and has stopped outside the bank.

1.47pm:UPDATE: Police and news helicopters have left the area.

1.36pm:UPDATE: Two men in dressed in black boiler-suits walking into the bank. Man led out and arrested.

Watford Observer: Watford alert: Man holed up in Co-Op bank

Two police officers took him to the other side of the road and put him into a van.

1.24pm:UPDATE: Several loud bangs heard near the scene...

1.05pm:UPDATE: Witness Johnny Matthews reported how his day took a dramatic turn. He said: “It was around 11am and police had a megaphone shouting for everyone to get out of the High Street.

There was a bit of a panic but most people seem to be quite calm about it and were listening to what the police were doing.

“It’s not what you would expect on a Thursday morning shopping trip.”

12.58pm:UPDATE: Police are pushing members of the public further and further down Market Street, leaving some business owners stuck in their offices.

John Marchant, a solicitor from Jeffrey, Doctors and Marchant, in Market Street, said: “We could hear the helicopters and when we looked out the window we could see people being pushed back and cordoned off by the police.

“The traffic has been brought to a standstill, we thought it must have been an escaped criminal but we went outside and they told us it was something at the bank.

“You wouldn't expect this to happen in quiet and peaceful Watford – maybe in central London.”

12.57pm:UPDATE:Sources say that the man at the centre of today’s alert initially entered neighbouring Natwest bank but fled when the emergency shutters were activated.

12.50pm:UPDATE: Police say they cannot confirm the nature of the threat posed by the man currently holed up in a Watford bank.

12pm Witnesses have reported that the man, who entered the Co-Op bank in Market Street at about 10.20am, has a bomb strapped to a part of his body.

Hertfordshire Constabulary, however, says it cannot confirm the nature of the threat posed by the man.

A man is currently holed up in a Watford bank.

Police were called at 10.18am this morning to the Co-Operative Bank, in Market Street, where the man was threatening to harm members of staff.

The street has now been cordoned off and a large number of police, including armed officers, remain on the scene as a police helicopter circles above.

A police spokesman said: “We have now been able to establish that this individual is on his own and no members of the public are at direct risk. Clearly, our objective is to resolve this situation as peaceably as possible and thank the public locally for their co-operation and understanding that this is a fast moving and complex situation.”

Traffic in the town centre has ground to a halt and the ring road is said to be blocked. Shoppers in the town centre have been placed behind a cordon at Charter Place.

Eyewitness: were you there? Text your updates and pictures or mobile phone footage to 80360 using WO as your subject line, or email reporter Neil Skinner