Police were told an alarm was going off at the scene of the Hatton Garden gem heist but decided not to attend, it emerged today.

Up to £200million of jewels were stolen in an audacious burglary over the Easter weekend, when thieves drilled into a vault at the centre of London's diamond district.

Police today confirmed that an alarm went off at the raided premises in the early hours of Friday morning, but they decided it did not need immediate investigation.

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Detective Chief Inspector Paul Johnson speaks outside Hatton Garden Safe Deposit Ltd yesterday. Police have admitted they were told an alarm was going off at the premises last week but did not attend the scene

Scotland Yard said it got a call at 20 past midnight on Friday morning from a company who monitors alarms across the South East.

A spokesman for the police said: 'The call stated that a confirmed intruder alarm had been activated at the Hatton Garden Safe Deposit Ltd.

'The call was recorded and transferred to the police's (computer) system. A grade was applied to the call that meant that no police response was deemed to be required.'

The spokesman added: 'We are now investigating why this grade was applied to the call. This investigation is being carried out locally.

'It is too early to say if the handling of the call would have had an impact on the outcome of the incident.'

Thieves disabled a communal lift shaft and abseiled down to the basement before using top-of-the-range power tools to break into the vault.

Once inside, they opened up to 70 safety deposit boxes in a raid described as 'sophisticated' by detectives.

After hearing the latest statement, furious jewellers branded police 'incompetent' for not attending when the alarm went off.

A call about the alert was categorised as not requiring a police response, Scotland Yard confirmed today. The raid was not discovered until Tuesday

The raiders are thought to have hid in an office before working their way down to the basement and drilling through a two-metre-thick wall into the vault and opening 70 safety deposit boxes

A 63-year-old trader, who asked not to be named, but had been in the business for 30 years, said: 'That statement now makes me so angry. How can they have ignored it?

'That line about "It is too early to say if the handling of the call would have had an impact" - What does that even mean?

'Do they even believe their own rubbish? What is this nonsense about it being a "sophisticated" raid? It's rubbish.'

Asked what he would do if his box was raided he said: 'The only option you have is to claim from your own insurance and the other possibility is to actually sue the owners of the building and the police.

WHEN DID THE HEIST HAPPEN? Thursday, April 2: Workers from businesses in the building go home for long Easter weekend. Some have claimed the thieves were already hiding inside the building waiting to be locked in. Friday, April 3: Police have found no signs of forced entry at the premises, but an intruder alarm sounded at the safety deposit business in the basement at 00:21. No police car was sent. Traders have claimed a security guard attended the site but said he 'wasn't paid enough' to look inside the vaults. Saturday, April 4, Sunday April 5 and Monday, April 6: The exact time of the raid has not been confirmed, but given the amount of time it would have taken to drill through the 2-metre-thick concrete wall and opened 70 safety deposit boxes, it is thought to have taken many hours. Tuesday, April 7: At 8am, workers return to the building and finding 'scenes of chaos'. They call the police, who attend. Advertisement

'Obviously I would need more information and I can't say right now what I will do but I would consider any of these options.

'Suing anyone is a last resort but it's something I would consider as a range of options.'

He added: 'I cannot believe that we actually pay these incompetent people. I say it is a waste of b****y time trying to get answers out of them.

'It makes you want to weep. We don't even know if our things are safe.'

Asked what he kept in his security box, he said: 'Listen, it's not even about that. I'm not even interested in talking about my possessions - they're valuable but I'm not interested in that.

'It's more to do with showing people some common courtesy. I've not received a call, I've heard nothing, and then suddenly I hear that they didn't even come out when the alarm went off on Friday.

'So far as I'm concerned the police have got a lot to answer for.'

Another jeweller and pawnbroker who runs a family business with his father, added: 'It's just unbelievable that they could ignore a call from an alarm company.

'That's the thing that gets me - you ask them for four days if they actually answered a call from an alarm company and they say some c*** about how they're "investigating" it.

'They're the ones who did it, so why do they need to investigate anything?

'The police have a lot to answer for.'

The police admission over the alarm came after potential victims had already expressed anger at being left in the dark over the investigation.

Many are still waiting to be told if they have lost out.

THE HILTI DD350 DIAMOND CUTTER: THE STATE-OF-THE-ART TOOL USED TO BORE INTO HATTON GARDEN The thieves used a £3,500 heavy-duty drill to make a number of holes in the reinforced concrete of the safe The Hatton Garden thieves used an expensive tool - the Hilti DD350 - to bore through a two metre thick wall of concrete and gain access to the deposit boxes. The tool is part of a group of products known as 'diamond core drills', which are used to burrow through thick concrete. Operating in a similar principle to a hole saw, they use a circular drill bit, lined with teeth, to cut a circle out of the concrete and are commonly used to create space for piping or manholes. Variations of the drills are also used in mineral exploration, where mining companies must drive through exceptionally strong natural materials thousands of metres below the surface. Hilti's product, which retails for £3,475, features 10 gears which can rotate the drill bit up to 667 times a minute. It also uses a water cooling system to prevent overheating, weighs 35kg and is marketed as 'high performance, low weight'. Advertisement

A 45-year-old jewellery dealer who only gave the name Sanj, said he could not believe that the police had not checked the building after an alarm sounded in the early hours of Good Friday.

'Obviously it's unbelievable that the police didn't come and check the building. I'm appalled.

'I think because the actual owners of the safe deposit are not here the police are taking it out on the rest of us. We have been in the building about a dozen times in the last few days.

'They are not telling us what's happened. A few people have been told, but the police aren't telling the others. It's like having a house burgled and being told to stay outside.'

He added: 'We're all taxpayers - the police are supposed to look after the public.'

Asked if he would consider suing the police or the storage company, he said: 'I think that's a legal decision.

'Our first port of call would be our insurance company.'

He refused to give details of what was inside his deposit box, saying: 'I wouldn't want to say - it's too sensitive.'

Speaking yesterday, safety deposit box owner Aadil Shaikh also criticised the apparent slow pace of the probe.

He added: 'We just want an assurance that they're doing whatever it takes to speed up the investigation and trying to track down those involved.'

He also expressed anger at the company which was burgled, adding: 'This is not a Third World country, it's London for crying out loud.'

Today a young man left the building looking close to tears.

As he walked quickly away, he said: 'I'm really not in the mood to give any statements right now buddy, I'm just really, really cheesed off.'

Calls to emergency services are dealt with by an operator who grades them 'in terms of their urgency', protocol states.

Met Police policy says: 'The operator will grade the call in accordance with standard operating procedures for the type of incident. The grading will depend upon the urgency of the call.'

Amid claims the thieves disabled and removed DVD-based CCTV cameras operating in the premises, OpenSky security director Nigel Stanley said using cloud-based camera technology would be a 'no brainer'.

He said: 'In this case over the weekend, the images would have been uploaded onto the internet as they entered the premises, so that evidence would have been captured.