The two-year anniversary of the vote to leave the European Union has come and gone. As the tick of the article 50 clock has built in intensity, months of speeches, negotiations and summits have come and passed. But, absurdly, it is only now that the prime minister has managed to align her cabinet around the beginnings of a Brexit vision.

The agreement she secured at Chequers was undoubtedly a political breakthrough for the Conservative party. Ever since David Cameron allowed ministers to dissent from the government’s position in the referendum debate, any semblance of cabinet unity on the biggest existential question facing the nation has been missing. An uneasy truce has – for now – been secured.

But it would be naivity to mistake it for a breakthrough in Britain’s national interest. The Chequers agreement does not begin to resolve the Brexit conundrum. EU negotiators have been unflinchingly consistent: in leaving the EU, Britain must confront a trade-off between sovereignty and access. It cannot cherrypick between the EU’s four single-market freedoms of goods, services, labour and capital, which the EU regards as indivisible.

There is now a chink of acknowledgement of that trade-off: the government has conceded that Britain will sign up to the EU’s regulatory standards for goods. But it wants the UK to be part of the single market in goods without signing up to free movement of services or people.

That’s not on the table: as the EU faces growing threats, from Trumpian trade wars to the rise of Eurosceptic populism, it will not dole out special dispensations that could lead to the single market, painstakingly constructed over decades, unravelling altogether.

May has also tried to square an impossible circle – maintaining no customs checks, and so no hard border in Ireland, while simultaneously being able to negotiate our own trade deals – with a proposal for a facilitated customs arrangement. Goods coming into the UK would be tracked, and different levels of tariff collected, depending on whether those goods stayed here or were moved into the EU. There are all sorts of questions bound up in this: does the required technology even exist? What about the potential for fraud? How could the EU allow this to sit for British manufacturers paying lower tariffs on imported components than their EU competitors but able to sell their products across the EU at unfair competitive advantage?

So May has strung together a fragile domestic political compromise only by confecting a solution that no one thinks the EU will accept. And even in the unlikely event that the EU were to sign on the dotted line, there is no disguising that while it may be better than dropping out with no deal, the Chequers agreement would be a terrible outcome for Britain.

It is a sop to the Eurosceptic ideologues on the right of the Tory party who harbour a pathetic nostalgia for a 19th-century manifestation of national sovereignty, back when Britannia ruled the waves. But that ideal of national sovereignty is long gone in a globalised, interdependent world buffeted by forces such as climate change and global tax avoidance that simply don’t respect national borders.

Acting alone, a country the size of Britain will always be a rule-taker, dwarfed by the world’s giant economies and big global trading blocs. But through its membership of the EU, Britain has punched well above its weight, playing a key role in shaping regulations that have led the way in establishing global standards, and which big multinationals based in countries from the US to China have had to follow. Now we are about to give up our say in shaping the rules of the world’s most successful trading bloc in the world in exchange for becoming a rule-taker in whatever scrappy free trade deal we can negotiate.

A free trade deal with a country like the US would undoubtedly come at a price: a race to the bottom on product standards, paving the way for chlorinated chicken and GM foods to flood the UK market. And even that is only a possibility if we sacrifice single-market access to the EU by dropping alignment with EU product standards. All the while, Brexit continues to absorb all available political bandwidth, while the big challenges facing the country – how we care for our ageing population; what we do about the large number of low-paid, low-skill jobs in the economy – linger unanswered.

So this is how the Chequers agreement should be viewed: not as some act of political mastermindery, but as a partial capitulation to a small band of ideologues who have never been able to articulate a convincing account of why leaving the EU would be good for Britain’s sovereignty in the 21st century. May should indeed do all in her power to get the best possible deal from the EU. But she should offer it up to the voters for approval and, for once, adopt an honest approach: here’s the best we could get if you do still really want to leave the EU, but there’s no way to do this that won’t seriously damage Britain’s interests.