Ukrainian President Volodymyr Zelensky is making his first visit to the UK since the Russian invasion of his country, with Rishi Sunak promising extra military support.
The Prime Minister announced plans to train Ukrainian pilots, paving the way for them eventually being able to fly sophisticated Nato-standard jets, a key request from Mr Zelensky.
Downing Street said the surprise visit would see Mr Zelensky meet Mr Sunak, visit Ukrainian troops and address Parliament.
He will also have an audience with the King, Buckingham Palace said.
The Prime Minister embraced Mr Zelensky as he arrived at Stansted Airport on just his second overseas visit since the war broke out – the president travelled to Washington in December last year.
“Since 2014, the UK has provided vital training to Ukrainian forces, allowing them to defend their country, protect their sovereignty and fight for their territory.
“It also underlines our commitment to not just provide military equipment for the short term, but a long-term pledge to stand shoulder to shoulder with Ukraine for years to come.”
The UK is also set to announce new sanctions targeting those who have helped Vladimir Putin build his personal wealth and firms which have profited from the war.
The expansion of the UK’s training programme to include jet fighter pilots is significant as Mr Zelensky has been urging Western nations to supply planes.
But the announcement by No 10 signals a shift for the future, and officials said that “as part of that long-term capability investment” the UK will work with Ukraine and international allies “to co-ordinate collective support to meet Ukraine’s defensive needs”.
Ukrainian troops are already being trained in the use of Challenger 2 tanks, which are expected to be sent to the country next month.
Mr Sunak will offer longer-range firepower to help counter Russia’s ability to strike at Ukraine’s towns and energy facilities.