Britain will this week sign its first defence cooperation treaty with Germany since the Second World War. Sir Keir Starmer and Friedrich Merz, the recently elected German chancellor, will both approve a pact promising their nations will assist each other if they are attacked. The symbolic move will be the centrepiece of Mr Merz’s visit to the UK, as the pair of relatively new world leaders try to develop a strong working relationship. The treaty is being seen as part of what some in Whitehall are calling an emerging “triangle” alliance between London, Paris and Berlin. The Prime Minister agreed to closer co-operation on nuclear weapons with Emmanuel Macron, the French president, during his state visit last week, telling reporters it was as important as the migrant small boats deal. All three countries have markedly increased defence spending since Donald Trump’s return to the White House in January threw the US’s long-term commitment to European security into doubt. The deal to be announced this week will also make it easier for German children to travel on school trips to Britain, boosting cultural and educational ties between the countries. Teachers will be able to bring pupils on visits without obtaining visas, according to the Financial Times, with lists of pupil names instead submitted en masse for speedy approval. The paper reported that officials hoped the step will help reverse an 80 per cent drop in German school trips to the UK since Brexit. Mr Merz, leader of the centre-right Christian Democratic Union once headed up by Angela Merkel, became German Chancellor in May. His visit is expected to include time spent at Chequers, the 16th-century manor house in Buckinghamshire which is the Prime Minister’s official country residence. It is the latest in a flurry of foreign leader trips to the UK this summer. As well as last week’s state visit by Mr Macron and Mr Merz’s trip this week, the US president is briefly stopping off at his Scottish golf course, Trump Turnberry, later this month. While the visit is largely taking place in a private capacity and is expected to be low-key, the Prime Minister is planning to travel up to Scotland to see Mr Trump. Discussions are also underway for Narendra Modi, the Indian prime minister, to visit in late July or early August, when the UK-Indian trade deal already announced will be signed. The bilateral cooperation defence treaty between the UK and Germany builds on last autumn’s Trinity House Agreement. It is expected to include a commitment for each country to assist the other if it comes under attack, according to government sources familiar with discussions. One Whitehall source said the agreement would be “an expression of the new British orientation towards Europe”. Sir Keir has talked up his “reset” with the EU since taking office. Both the UK and Germany are already members of Nato, whose Article Five says an attack on one member is considered an attack on all. It is unclear exactly what the new bilateral commitment provides beyond that pledge. At the very least, it is a symbolic declaration of how closely German and British security interests are tied together in the face of an expansionist Russia. The increased talk in Whitehall of a “triangle” alliance between the UK, France and Germany comes with the backdrop of Mr Trump’s vocal criticisms of European partners and their track record on defence spending. Mr Macron laid out the case for both the UK and France becoming less dependent on America as well as China when he addressed a joint session of Parliament last week. The French president said: “We will have to de-risk our two countries from the excessive dependencies on both the US and China. He added: “If we still depend on both China and the US, I think we have a clear view of our future and the future of our children.” Spokesmen at multiple UK government departments declined to comment on the specifics of the agreement, noting discussions about the deal were still underway.