We live in a world of corporate goliaths and the trend to gigantism is accelerating. The new era of hi-tech data capitalism has an embedded proclivity to monopoly. The bigger the network, whether Facebook or Google, the more valuable it is to be connected. Big is good in the digital universe, while even bigger is better.

Meanwhile, analogue capitalism, confronted by the challenge of the new, is reacting by consolidating and merging into ever larger entities. Unless they do, comes the reply to any challenge from national competition authorities, they won’t have the heft and scale to meet the new competition. Increasingly, we are surrounded by the most awesome concentration of corporate power in the history of capitalism. In every industry, reported the Obama administration last year, the market power of the biggest companies has been growing and mark-ups and profit margins with them. America’s era of the robber barons in the late 19th century had nothing on this.

Last week came another small milestone, in Britain. Hammerson, a property company few will have heard of, swooped on its rival, Intu, even less well known, in a £3.2bn bid. Yet the outcome will affect us all. Many major shopping malls – London’s Brent Cross, Birmingham’s Bullring, Manchester’s Trafford Park, Oxfordshire’s Bicester Village – will be owned by the same company. Hammerson will be the arbiter of how we shop: what stores are positioned where, in what mall and at what rent; it can even determine the restrictions on forms of permissible public activity in its private spaces.

Hammerson will argue that it had no choice. So much shopping is online that the mall is looking increasingly like a late 20th-century phenomenon, outdated and outmoded. E-shopping is booming and, with the advent of virtual reality, you can go beyond browsing online to “handling” the goods you plan to buy. Hammerson’s only option is to buy up its competitors and try to hold the digital invaders at bay. You can see its point, but its monopolistic grip on the market will be such that it is better empowered to resist declines in rent and will take any opportunity to lift them. Our competition authorities stand idly by, helpless onlookers rather than proactive interveners.

Birmingham’s Bullring shopping centre is now owned by Hammerson after its takeover of Intu. Photograph: Bloomberg/Bloomberg via Getty Images

Meanwhile, the digital invaders are getting bigger. One of the laws of economics, itself an analogue discipline teaching doctrines far removed from the realities of today’s markets, used to be that as companies grow they start to lose control of their capacity to be efficient and unit costs rise. This is called decreasing returns to scale. In this way, or so the theory went, we could trust a free market not to produce corporate goliaths because they become inefficient, the ideology that Brexiters so blindly believe. But one of the features of data capitalism is exactly the opposite: increasing returns to scale. One of the attractions of Facebook, Spotify, Uber, Amazon or Airbnb is their very size. Their managers don’t lose control of their operations as they grow. Indeed, computerised techniques allow costs, from wages to the organisation of production lines, supply chains and warehouses, to be ever more efficiently managed.

From the users’ point of view, the bigger the network and search engine the more efficient it is to use: Google is the search engine of choice because of its scale; similarly, Uber, the ride-hailing app; Facebook, the communication channel, and Airbnb, the means to find a room. In every case, the sheer size of their network means we get the best results. On top of this, they take over rivals. Facebook has bought WhatsApp, Microsoft owns LinkedIn, and Google acquired YouTube, along with a host of small companies destined to be potential challengers but that were devoured. Thus today’s capitalism: corporations are growing ever bigger in the new and old economy alike. In the new economy, they hold more and more personal information and data about consumers; in the old, they hold ever more market power. Profits as a share of GDP in advanced industrial economies are rising and, with them, share prices and directors’ remuneration; wages and job security are declining. Globalisation has become a universe of monopoly, oligopoly and shadow cartels. Prices are not fixed in smoke-filled rooms: the market leader in whatever global industry sets a reference price that everybody follows tacitly – or faces dire consequences.

This is a far cry from the imagined world of Brexiters, where supranational authorities and regulations, especially EU regulations, are “shackles”. National competition authorities are all that are needed to ensure free and fair competition; virtuous global enterprise is rewarded and policed by the World Trade Organisation (WTO), the fabulously effective and universally revered global trade referee. All Britain has to do is champion free trade outside the sclerotic EU under WTO rules and it will be blessed with a new age of growth and prosperity. In reality, competition and anti-monopoly authorities are no match for the behemoths and the WTO is systematically gamed and undermined by the two economic superpowers. The US, the Brexiters’ great buddy, is refusing to nominate judges to the WTO’s appeal court; instead, it takes on China unilaterally for alleged trade abuses. The WTO is weak and getting weaker.

International trade is not a game of cricket between equally matched teams, only disturbed by Brussels Eurocrats, as Jacob Rees-Mogg, Boris Johnson et al imagine, waiting for a Britain, energised by leaving the EU, to further stimulate it. It is a dog-eat-dog world in which the choice for a medium-size country is to make common cause with one of the three economic blocs capable of challenging the new monopolists and cartels – China, the US or the EU – or roll over and be plundered. Britain alone has no chance of challenging the West Coast tech giants over their policies on anything from tax to data or challenge any of the analogue goliaths over their stance, say, on diesel emissions or plastic packaging.

You don’t have to be a Marxist to worry about where today’s capitalism is heading – both the Bank of England and the Economist magazine share the concerns. But it is curious that Labour’s allegedly leftwing leadership is so quiet. Far from a capitalist plot, EU membership is one of Britain’s few available defences. Trade unions understand this well: it is time for Jeremy Corbyn and John McDonnell to find their voice. Leaving the EU can and must be stopped.