The British political system likes to present itself as one where power shifts decisively from one party to another. The removal van arrives in Downing Street, and a very different government replaces the defeated one. These quick, dramatic switches are meant to be one of the good points of our system: the electorate’s wishes clearly enacted, in compensation for being kept at a distance from centralised Westminster the rest of the time. It’s in the interests of the two big parties sustained by this system to say they offer a stark choice. And sometimes that’s true: Jeremy Corbyn’s loose socialism against Theresa May’s stern Conservatism; Keir Starmer’s self-conscious competence against Boris Johnson’s showy chaos. Since 2015 the gap between Labour and the Tories – in style, ideology and policies – has often been larger than ever. Yet recently, without being widely noticed, the gap has been closing. In some striking ways, Starmer and Rishi Sunak are similar politicians. Both are relatively inexperienced, elected as MPs only in 2015. Both are better at paperwork and preparation than spontaneous communication. And both present themselves as realists, clearing up after unrealistic predecessors. More disorienting still for anyone who takes the rhetorical battles between the parties at face value, the Conservatives are increasingly adopting Labour policies: an energy price cap, a windfall tax on energy companies, and raising state benefits in line with inflation. This week, the Tories made a policy announcement that copied a Labour proposal almost word for word: promising to “make the right to request flexible working a day-one right” for all employees. Labour called for “the right to flexible working for all workers … from day one” back in July 2021. During this year’s first Tory leadership contest, Sunak pledged: “I will govern as a Thatcherite.” Yet now he leads a government that raises taxes, emphasises how “compassionate” it is, and has hired the former senior New Labour figures Patricia Hewitt and Michael Barber as advisers. In the rightwing press, and on the right of the Tory party, there is disbelief, and loud grumbling, that Sunak is governing like Gordon Brown. In some ways, you could argue, the transition to a Labour government has already begun. This blurring of the lines between the two parties should not be a surprise. Gradual transitions between a fading government and its likely replacement actually happen quite often in Britain. In the 1970s, Jim Callaghan’s Labour administration adopted monetarist economic policies before Margaret Thatcher did. In the 1990s, John Major’s optimistic talk of “a classless society” anticipated Tony Blair’s attempt to make Britain into a meritocracy. In 2010, Brown’s chancellor, Alistair Darling, proposed “tough” cuts in public spending that prefigured George Osborne’s austerity. This trade in ideas, language and political tone between parliamentary enemies is neither straightforward nor often openly acknowledged, nor necessarily even conscious. As well as simply stealing policies from the opposition in a bid to change just enough to blunt its criticisms, placate enough voters and thereby cling to power – which is the strategy Sunak seems to be following – old governments can also be groping for ways to reflect new times. The rightwing papers may still believe Britain can be saved by market forces, but to be a Tory minister now is to be faced with endless market failures. Sunak is one of the biggest enthusiasts for capitalism in his party, yet even he conceded in a lecture this year that “the market has limits”. The problem with such ideological retreats, from a government point of view, is that they can be an unintended admission that a change of regime is required – or even a sign that some in the ruling party are starting to give up. The silences and absences on the Conservative benches in the Commons under Sunak suggest the latter. Government retreats can also normalise the opposition’s policies and rhetoric. Starmer can talk about price caps, new taxes and creating “an economy that works for working people” with a degree of boldness that Brown and Blair never dared – despite their greater confidence in other areas – partly because Sunak is the fourth Tory premier in a row to acknowledge that our economic model is in trouble. In theory, this normalisation of concerns about capitalism could enable Starmer to move further leftwards. Now that both main parties agree on intervention against profiteering energy companies, Labour could advocate action against other businesses that have greedily increased their margins. A recent analysis by the trade union Unite found that “profit margins for the UK’s biggest listed companies were 73% higher in 2021 than … in 2019”, and that this surge has continued into 2022. Given that most Britons are getting poorer in the cost of living crisis, to which this profiteering has substantially contributed, further windfall taxes or price caps might be socially and economically beneficial, and highly popular. But Starmer and the shadow chancellor, Rachel Reeves, are instinctively cautious. A more likely consequence of the Tories’ shameless pilfering of their policies is that these policies will be thoroughly tested in practice well before Labour gets into government. A Tory government acting as a laboratory for a Labour one: after all the decades of Labour accepting Tory policies, that would be a pleasing irony. Labour supporters shouldn’t get too carried away, though. Under Starmer, the policy trade between the two parties has not just been one-way. On Brexit, Ukraine, defence and anything else deemed “patriotic”, Labour remains deferential to the Tories: largely accepting their positions and their definitions of what matters. If Starmer wins the election, his acceptance of reckless Tory stances, for example on Brexit, may undermine his government, just as New Labour was ultimately undermined during the financial crisis by its acceptance of the oversized City of London that Thatcherism had created. Ideas inherited from other parties can be poison pills. That said, we should not overestimate Starmer’s common ground with Sunak. On probity in public life, private schools, poverty and wealth, whom the economy should prioritise, social values and the environment, Labour and the Tories remain miles apart. The period until the next election, and the election itself, are likely to be acrimonious as a result. When fading governments steal ideas from their opponents, it’s usually a sign that their diehards will do anything to stay in power. Andy Beckett is a Guardian columnist