Sir Julian Brazier is a former Defence Minister, and was MP for Canterbury from 1987-2017. He is Chairman of a security company.

All eyes are on the foreign policy implications of the Soleimani assassination, but the incident also demands a look from the other end of the telescope – at how Britain should address homeland security.

Salisbury has seen a chemical attack by the Russians. In Manchester, London and elsewhere Sunni Islamists have struck. A neo-fascist has assassinated an MP and the assassination reminds us of the threat from Tehran’s Shiite fundamentalists.

The government is due to conduct a Defence and Security Review and has a strong cast of professional advisers to assist it. But any examination of homeland security – a key strand of that review – should start by accepting a premise which is deeply unpalatable to most such advisers; the conventional arms of the state can do very little more to protect against some of the worst threats the public faces.

To take some examples. A lone, and so far unnoticed, individual who has acquired the skill to make an effective bomb (or even is able to steal a lorry) is unlikely to be spotted by our intelligence services, excellent as they are. Yet a lone bomber killed 23 and injured far more at Manchester Arena in 2017.

At a time when desperate – and poorly resourced – migrants can cross the Channel undetected in inflatable boats, a terrorist unit, with an arsenal of weapons could slip into any of our hundreds of marinas, in a yacht, with little risk of detection, by the Royal Navy, Coastguard or Border force.

Misha Glenny outlines in his book MacMafia how ex-spetsnaz Russian hitmen regularly fly to Britain, kill the targets of Russia’s state and crime bosses, and leave before the body has been found.  The Skripal case was arguably only unusual because the means (chemical warfare) and the choice of target (a prominent defector) led Mrs May’s government to take international action.

What can we do about this? Extra full-time manpower and assets for existing government agencies cannot provide a solution. If all the extra police officers the government plans to recruit were to be directed into protecting public events and places, from football matches to music festivals to crowded shopping centres – abandoning cherished plans to crack down on conventional crime – the effect would be marginal. 10,000 extra bodies – on shifts and with holidays – would not go far.

The reality is that most of those elements of security are, and will continue to be, provided by the private sector. But, if the private security industry is to be effective in countering terrorists, it needs a closer relationship with government on everything from training qualifications (which are not fit for this purpose) through to planning and legal issues.

At sea, we used to have various volunteer forces including an afloat section of the Coastguard – today their only volunteers are the excellent Rescue Service (which focuses on coastal work like cliff rescue and countering beach pollution). If we restored the afloat branch, drawn from yachtsmen, fishermen, ferry staff and others who spend their work or leisure time in our territorial waters, they could be used to watch out for suspicious behaviour. Introducing drone patrols could capture every small boat movement, but the Border Force cannot possibly patrol every marina and tiny port. Having a large pool of trained volunteers who watch out for suspicious arrivals in yachts and small cargo vessels greatly increases the chances of detecting those who wish us ill.

One cheap and highly efficient facility is the National Maritime Information Centre which integrates information from the armed forces, intelligence services, coastguard etc near Portsmouth. This would be so much more effective if it could harness a large pool of volunteers who spend time around our coastline and – crucially – have some training and direction in looking for the bad guys. A similar organisation based on flying clubs could help with the vulnerability of our small airstrips to incursion by terrorists and organised crime.

Ruth Edwards’ imaginative proposals for boosting cyber security in the commercial world would fit well with such a strategy, but we also need to expand the cyber reserves – so that the critical elements of the state can rely on an affordable and top quality surge capability when a large-scale threat emerges.

More widely, if a serious incident takes place, the default position is to use armed police and, if they are unable to cope, call in Special Forces. This is fine provided incidents come in ones or twos and are well-defined – for example bombing or shooting or stabbing incidents. Salisbury showed how much more resource is rapidly absorbed by a more sophisticated attack.  To cope with some kinds of incident, hundreds or even thousands of soldiers may be required to cordon and search or lock down a large area – and the perpetrators of the Salisbury incident were just one very small team.

A capable and well-resourced enemy might well start a number of diversions in cities before making his main attack – or attacks – hundreds of miles away, perhaps with chemical weapons or just an imaginative use of explosives across a range of locations. A cyber dimension could make a bad situation much worse and quickly.

So, there needs to be a backup on the ground. At present that is provided by the Regular Army but, excellent though our army is, it is now largely concentrated on a few giant sites, like Tidworth and Catterick, a long way from our major cities. Yet there is no substitute for local knowledge in an anti-terror operation, as the Ulster Defence regiment showed in the Northern Irish troubles.

The Americans rightly call out their National Guard for this kind of work and the Houghton Report, Future Reserves 2020, in 2011, recommended that our Reserve forces, with 350 centres up and down the country, be used in this way.

At the macro level, there is a serious danger that the next Defence and Security Review will try to address some of these issues by shifting resource away from our depleted deployable forces to provide more paid professional people working in homeland security. I hope I have shown that this would achieve little. A few extra patrol boats would enhance coastal security – and perhaps help police the post-Brexit fishing regime – but go nowhere near filling the gaps in our coastline. Further expanding our excellent intelligence services would only marginally increase the small proportion of suspects who can be kept under observation at any one time.

And squeezing still further the budget for deployable forces to pay for such items hardly seems wise. Does anybody believe that we need less warships to cope with the kind of situation which is emerging in the Straits of Hormuz or for that matter the South China Sea? Our tiny air force, with just eight remaining combat squadrons and small army with its aging equipment are hardly sensible targets for cuts in a dangerous world either.

Ben Wallace was right to point out on Sunday that we may not be able to depend on the United States indefinitely. If that is the case, we shall have to expand all these forces.

Instead we should return to a critical theme of the 2010 review – the Whole Force Concept: regulars and civil servants (the state professionals) alongside reserves and contractors. This theme almost disappeared from its 2015 successor.

What is needed to make us safer is to harness a much larger part of the population, beyond government full-time professionals, bringing in the reserve forces, new – and existing – volunteer groups and private sector security.

Security needs to become a responsibility of the nation, not just government’s professional forces. At the Fishmongers Hall a small group of gallant people and the volunteer organisations who responded – before and after the Police – showed us that some at least, in this great nation, are up for it.