Steinmeier enjoyed a horse-drawn carriage ride with King Charles III and inspected a Guard of Honour at Windsor Castle, west of London, on day one of his three-day stay.

He was feted with a 41-gun salute at the 1,000-year-old castle where he ate lunch and reviewed items related to Germany in the Royal Collection.

Steinmeier then met UK Prime Minister Keir Starmer at Downing Street, where the British leader praised the work the two countries had done supporting Ukraine.

Starmer said Britain and Germany were also working together on migration, trade and economic growth and that the two countries' relationship was going from "from strength to strength".

The German president said relations between Berlin and London were now in "far better shape" than in the "difficult" years after the UK voted to leave the European Union in 2016.

"We have to engage in improving the situation and coming closer in this changing world with new threats to all of us," he told Starmer.

The trip, which includes a state banquet and a speech to parliament, takes place as a deepening security alliance has helped rebuild London-Berlin ties that frayed in the turbulent post-Brexit years.

Charles visited Germany in 2023, in his first overseas trip as monarch.

Steinmeier's plane landed amid tight security at London's Heathrow Airport, where he was greeted by heir to the throne Prince William and his wife, Catherine.

Steinmeier was foreign minister when the Brexit referendum occurred and had choice words back then for the "irresponsible politicians" who "lured" Britain into leaving the EU.

However, ties across the Channel improved under Conservative prime minister Rishi Sunak, and the trend has continued under his centre-left Labour successor Starmer.

The visit comes as both the German and British governments face pressure from hard-right, anti-immigration parties -- the Alternative for Germany (AfD) and the Reform UK Party led by Brexit cheerleader Nigel Farage.

- 'Apprehension' -

Russia's 2022 invasion of Ukraine and the political turmoil unleashed by the Trump administration have led key European powers to forge closer ties, including World War I and II-era foes Germany and Britain.

In October 2024, western Europe's two biggest military spenders signed a defence pact, followed by their first "friendship treaty" in July.

"The core of the relationship is in the security and foreign policy field," said Nicolai von Ondarza from the German Institute for International and Security Affairs.

But despite closer ties, Ondarza told AFP that "the UK is still much less present in German political debate than it has been in the past".

In Berlin "there is an apprehension that the current Labour government won't be courageous enough to move further on cooperation with the EU", he said, as Farage rises in the polls.

The friendship treaty also included agreements on preventing irregular migration and promoting cultural and educational exchanges.

- Bombed cathedral -

History will feature prominently in Steinmeier's visit, which on Friday takes him to Coventry, a city devastated by German air raids in World War II and twinned with Dresden, which suffered a similar fate at the hands of the Allies.

Steinmeier will lay a wreath at the bombed-out ruins of the city's old cathedral, joined by members of the Luftwaffe and British servicemen.

He will then travel to the university city of Oxford to receive an honorary doctorate and visit a subsidiary of German industrial giant Siemens.

Representatives from Siemens and several other heavyweight German companies such as BMW, Deutsche Bank and RWE will join Steinmeier's delegation.

Mercedes is set to announce a pound20 million ($26.4 million) electric vehicle technology project expected to create 150 jobs in the UK.

The countries' shared passion for football will be reflected on Thursday when German stars Per Mertesacker and Kai Havertz join Steinmeier to visit a London school.

jsk-mp-pdh/jkb/phz

Siemens

BAYERISCHE MOTOREN WERKE AG

Deutsche Bank

RWE

Mercedes-Benz Group