The lure of of Isis will not be stifled by the building of walls

The trench being built by the Tunisian government will be as useful as sticking a plaster on gangrene

A security guard in Sousse, Tunisia where a state of emergency has been declared (Fathi Belaid/Getty)

Building a wall along a border won’t change a mindset. Thousands of holidaymakers are being flown home from Tunisia, and the effect on the country’s economy will be devastating. Innocent people will lose their jobs in the tourism industry and it will take years to persuade visitors to return and spend their cash in one of North Africa’s most welcoming and lovely spots.

Faced with the threat of further atrocities, the Tunisian government has decided to take drastic action. To stem the constant flow of disaffected youth across their porous western border into Libya – where they receive training and weapons to join militant Islamists – a wall is to be built. It will stretch for 104 miles, from the Mediterranean in the north to Dehiba in the south and will have trenches on either side, and watchtowers at regular intervals.

This wall will be as useful as sticking a plaster on gangrene; it will achieve absolutely nothing, and is a piece of macho posturing by politicians who can’t think of anything better. Throughout history, rulers have built walls to try to hold on to power and keep out invaders, aiming to keep their subjects unsullied by unacceptable doctrines. North Korea is a prime example of a wall which will fall any day now.

In the 21st century, walls are an archaic way of controlling movement, particularly when so much warfare is managed online and in the air, using remotely controlled drones, and when you can tour the world via a screen. Barriers like the Chinese Great Wall, and the Roman Emperor Hadrian’s attempt to shut out the Scots, look heroic in their ruined splendour (and are fabulous to walk) but they achieved very little. Walls can’t stifle thought or prevent counterculture and revolution. In fact, walls make what’s on the other side seem even more attractive.

Undeterred, the Hungarians are building a fence along their 109-mile border with Serbia, a route used by refugees fleeing the Middle East en route to Austria and Germany. In the UK, we have miles of coast and dozens of ports, a border that is increasingly hard to police, with the Channel Tunnel and the cross-Channel ferries a flash point. So David Cameron has authorised a few million to be spent on – clearly inadequate – reinforced fencing in Calais. As the number of refugees rises, and following deaths in the Channel Tunnel, we know people will stop at nothing to break through barriers and reach the UK.

Meanwhile, Israel is building a 430-mile-long barrier to keep out suicide bombers from the West Bank, and Saudi Arabia is building a 600-mile wall to block out Iraqi refugees. All this wall-building, and yet the fence between the US and Mexico has been completely ineffective at preventing illegal immigration. So ineffective that President Obama has declared an amnesty to legitimise immigrants, mostly from Mexico, living in the US without papers. Under the new rules, up to 3.5 million people will be eligible to receive social security numbers, and pay taxes.

The British patrolled the border between Northern Ireland and the Republic, but did it really prevent sectarian violence?

The lure of the repulsive philosophy of Isis will not be stifled by the building of walls, just as the lure of work in Western Europe will always appeal to people fleeing violence and poverty.

Some food for thought for the Chancellor

George Osborne says he wants to give kids a better start in life, but his Budget omitted to extend one radical policy introduced by the Coalition which really would make a difference. The Chancellor should have provided funding for compulsory free school meals for all. Since the introduction of free meals for pupils up to the age of seven, there’s been an 85 per cent take-up.

The Government must ban packed lunches and insist all councils refuse planning permission to fast food outlets within a mile of any school. Forget human rights and choice, the child obesity crisis would be nailed if my radical proposal was adopted. Choice allows gangs and groupings to emerge in the playground.

Eating together means pupils have to develop relationships and social skills. Make cookery compulsory from the age of six and introduce after-school classes for young mums and dads. I spoke at a conference organised by the providers of school meals this week; they fret that cuts to funding will have an impact on their services. But surely the savings to the NHS if our children are healthier will balance the books. The benefits to their education are unquestionable – children need routine, and the discipline of sitting and eating together. It’s not about class or income, but about building a community.

You don’t need a super-yacht to enjoy a summer dip

Roman Abramovich has been touring the beautiful Western Isles of Scotland on his super-yacht, disembarking for dog-walking and cycling. I cruised the same route a few years ago (not on a super-yacht) and managed to swim off every island, from Oban to Harris, North and South Uist and Skye, dodging seaweed, jellyfish and icy waves.

They were some of the most invigorating and memorable experiences of my life. Nothing compares to wild swimming – this week I’ve managed four dips – the best of which come at sunrise, on a clear and still morning.

Abramovich is also a swimmer, but – inevitably – needs a special kind of pool. Applying for planning permission to extend his huge London home in Kensington, he claimed that the existing pool was “miserable”. Apparently it has a low ceiling and must be replaced with an imposing, vaulted and tiled structure inspired by Victorian underground architecture.

Abramovich claims this pool will be more “inspiring” – which actually means it’s just a lot bigger. Why doesn’t he save himself £20m and jog over to Kensington Gardens for a swim in the Serpentine – a far “happier” eco-friendly experience in the open air which costs very little.

As if life in North Korea weren’t hard enough...

My first pet met an untimely death which remains an unsolved mystery. Terry the Terrapin lived a pampered life inside an old enamel washing-up bowl by the rockery in our tiny back garden in inner London.

One day I rushed home from school to find Terry on his back, legs floppy and head slumped on one side. My mother blamed a local cat, but I suspected the boy next door, who later turned out to be a violent gangster.

A good job I didn’t grow up in North Korea, where the world’s most bizarre dictator executes anyone (around 70 victims since 2011) who incurs his displeasure – and now a terrapin-owner has been deemed disloyal to the state. His crime? The creatures he was rearing lay dead in their tanks when the Dear Leader made an impromptu visit.

Constant power cuts (a regular feature of daily life in North Korea) make life unbearable for humans, let alone terrapins, and lack of food made the task of breeding these creatures extremely challenging. When the pumps delivering fresh water to their tanks failed, they met the same fate as my Terry.

Kim had a major meltdown, and the hapless terrapin-breeder was put in front of a firing squad. Under-performance and lack of productivity is a recurrent concern expressed by our business leaders, but I’m glad there’s no danger of adopting the Dear Leader’s remedies.