Sir Julian Brazier is a former Defence Minister, and was MP for Canterbury from 1987-2017.

The Government is surely right to stick to its deadline for leaving the EU – any slippage would give Brussels a strong incentive to keep talking and enjoy us paying by the day for the extension.

It well understands that negotiation can only work if we are seen to be willing to walk away and is reportedly stepping up plans for No Deal. Yet an area which has not figured much in published plans, but will be critical if there is no deal, is retaking control of our territorial waters. This will be important for dealing with issues ranging from fishing to illegal immigration.

Take fishing first. Without a deal, there is a danger that the governments of countries with large fishing operations in British waters simply refuse to assist us in upholding the new legal status quo.

Despite eye-watering financial pressures, the Royal Navy has managed to expand its fleet of offshore patrol vessels to eight, but one of these is always committed to policing the Falklands and one or two more are usually being refitted or repaired.

This is a tiny force if we were to be faced with the vast French, Spanish and other fishing fleets ignoring the new legal position and continuing to fish. Our Exclusive Economic Zone (EEZ) has an area almost three times that of the UK.

In the Cod Wars of the 60s and 70s, despite flagrant breaches of international law by the Icelandic coastguard, Royal Navy vessels were forbidden to fire on the vessels of our NATO ally. RN warships came off badly in collisions with Icelandic coastguard vessels with their commercial hulls.

Today, modern warships, expensively built for speed and refined to minimise radar and sonar signature, are even less of a match for a brush with the trawlers who fish our waters – assuming they are not allowed to open fire. It is sobering to remember that we lost all three Cod Wars – and much of our fishing industry – at the hands of tiny Iceland.

One answer is the deployment of Royal Marine boarding parties by helicopter. This could indeed be done a few times, but the potential scale of the task and the distances involved would be logistically challenging.

Worse – assuming again the Government forbids the use of lethal force – would be the risk to the lives our gallant Marines. Trying to board, perhaps in heavy sea states, vessels equipped with high pressure hoses and manned by hostile crews would be a dangerous activity, raising issues on the moral and legal duty of care. Public opinion would understandably turn ugly with fatalities.

It is important to understand that the fishermen concerned (they are still overwhelmingly men) would be seen as heroes in their own communities, standing up to the British for their way of life and for access to grounds they have fished for two generations. A great deal of investment has gone into their vessels – much of it government money, in the case of Spain.

The French and Spanish governments, still staggering under the economic effects of the Coronavirus would have a strong political incentive not to assist us in dealing with such wholesale lawbreaking. Yet if we did use lethal force, and fishermen desperate for their livelihoods continued to resist, the diplomatic consequences are difficult to exaggerate.

Fortunately, the Icelandic coastguard demonstrated – illegally in their case – that there is another way. Small but robust fast craft equipped with equipment to cut lines, can put a fishing boat out of business, for a whole mission. There is a slight risk to life to life and limb but a far smaller one than opening fire.

To open up this fresh option, however, we need to buy and convert such vessels now to supplement our flotilla of patrol vessels. They do not need to be expensive – the support fleet for the declining North Sea oil industry offers cheap options for second-hand purchase, for example. If we were seen to be investing in such vessels, to work alongside the Royal Navy’s patrol vessels, it would send an unmistakeable message to Brussels that we are serious in the negotiations.

The issue goes well beyond fishing. News of the coronavirus has largely suppressed coverage of the steady trickle of illegal immigrants across the Channel, arriving in small craft. For some years we have benefited from active assistance from the French authorities, catching some craft and returning the occupants to France. They have also patrolled some beaches at night, disrupting the activities of the organised crime gangs responsible.

This has been in the French national interest as it helps the country avoid becoming a magnet for illegal migrants hoping to make their way onward. Nevertheless, one suspects that many French people do not welcome the trickle of returnees and anecdotal evidence is emerging that such cooperation is already starting to disappear. After a breakdown in negotiations, attitudes are likely to harden further.

Are we going to simply accept the trickle turning into a flood next summer, and with no prospect of return to France? Quite apart from undermining one of the cornerstones of our approach to immigration, it would make a mockery of our measures to combat corona virus through restrictions on international arrivals.

Of course, we need legal changes so such people can be held, rapidly processed and in most cases deported to their home countries. The word is that Priti Patel is planning for that, despite Home Office opposition. Nevertheless, without more vessels, that approach is likely to be undeliverable.

A related subject is international terrorism. So far terrorists have not made much use of our weak coastal security but that could easily change. In an earlier article, I called for the setting up of a new volunteer force drawn from those who work and enjoy their leisure at sea to provide intelligence. To respond to intelligence, we need a larger force than the tiny flotillas of Royal Navy patrol vessels and UK Border force cutters.

If we make no preparations to reclaim our territorial waters, our EU counterparts may well conclude that we are blustering. They may decide that we cannot realistically protect our EEZ anyway – and that they will have considerable leverage after independence as we will continue to depend on French good will in the Channel.

Conversely, taking modest public steps to fill this gap, will send an unmistakable message to our EU counterparts that Britain means business.