Security chiefs have issued a stark private warning to the government that Britain’s counter-terror forces must be significantly boosted if they are to cope with a Paris-style terrorist attack.

The message has been delivered to the chancellor, George Osborne, before a strategic defence and security review to be announced by David Cameron on Monday. The Observer has learned that Osborne has been planning a £200m cut to proposals for the review made by Scotland Yard’s counter-terrorism command.

Senior officers have stressed the importance for the Treasury to make a U-turn in the wake of the atrocities in Paris that led to a loss of 130 lives, and the growing threat from Isis. Writing in this newspaper, Lord Blair, the Met’s commissioner at the time of the 7/7 bombings, puts further pressure on Osborne by warning that “governments fall” when they fail to protect their citizens.

It is understood Scotland Yard has told Osborne it requires a significant increase in the number of armed patrol vehicles at an estimated cost of £80m in the first year, then £62m annually thereafter.

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Scotland Yard believes that the evolving danger also calls for a boost in the numbers of specialist firearm officers, at a cost of £15m in the first year, reducing to £13m annually.

Whitehall sources said Scotland Yard had also requested access to RAF Chinook helicopters, and investment in greater intelligence gathering and link-ups with police forces in northern Europe. It also wants the Treasury to rethink its plans to “back-load” counter-terrorism funding across the next five years, insisting that Scotland Yard needs significant resources this year and next.

The appeal from Britain’s counter-terrorism chiefs, amid growing fears over the Isis threat, forms part of an urgent review of tactics that was first drawn up in January at the time of the attack on the offices of Charlie Hebdo magazine.

On Saturday, Brussels was put on the highest terror alert level after Belgium’s prime minister, Charles Michel, said that intelligence led them to fear an imminent Paris-style attack. The Belgian capital was in lockdown, with soldiers on the streets, shopping centres closed and sporting events and concerts cancelled.

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Cameron will travel to Paris on Monday for a meeting with President François Hollande at the Elysée Palace. A Downing Street spokesman said: “They are expected to focus on counter-terrorism co-operation and the fight against Islamic State in Syria and Iraq.”

Police concerns about the impact of mainstream policing cuts on this country’s defences were also revealed last week in a letter leaked to the shadow home secretary, Andy Burnham.

The letter, sent by a senior police chief after an emergency Cobra meeting last Sunday, warned the home secretary, Theresa May, that the police had “already seen a reduction of 40,000 officers and further losses will severely impact on our surge capacity”. It has been reported the Treasury has been looking for a 20% cut to police budgets.

The Observer has since learned that the Met Police commissioner, Bernard Hogan-Howe, wrote to the chancellor last week to ask for extra funds in the National and International Capital City grant, which is designed to reflect the additional dangers for London.

Blair, a cross-bench peer who was Met commissioner between 2005 and 2008, delivers a devastating critique of the government’s handling of the police.

He writes: “Somewhere in government, someone powerful does not understand that intelligence does not only emerge from the supercomputers of GCHQ but from quiet, patient police work in communities.

“This is the most perilous terrorist threat in our history. The British police, with their long successful track record in counter-terrorism, have adapted well to the changing circumstances and, at the last moment, the very best defences they have built, the neighbourhood teams and the fast and accurate response to multi-site concurrent attacks, are being downgraded. People die this way. Governments fall. Remember Madrid in 2004 and think again.”

Blair further illustrates his concern by citing a potentially key point during the investigation into the failed bombings of 21 July 2005, in which council workers found evidence of bomb-making in a block of north London flats but did not know where to pass on the information.

He writes: “It was not found because the roll-out of neighbourhood policing had not reached that area by that stage. The teams are there now, although attenuated. Soon they will be gone.”

A YouGov poll published on Saturday shows that 70% of British adults believe that the government’s planned reductions in police officer numbers will compromise the fight against crime.

Only a fifth agree with Cameron that police can be cut further with no impact on service. The poll also shows that more than half of respondents say they see local police out and about less than five years ago, while only 7% think police are more visible than they used to be.

Jack Dromey, the shadow policing minister, said: “For David Cameron to claim that over 20,000 more officers can be cut on top of the 17,000 that we have already lost without impacting on public safety is quite frankly irresponsible, and now we know that the public do not believe him.”

A Treasury spokesman said: “We’re not going to comment on speculation ahead of the spending review. The PM is laying out the details of the SDSR on Monday and the chancellor will deliver the spending review and autumn statement on Wednesday.”