"This is a really significant deal, because it's pound8 billion ($10.7 billion) worth of orders... these are jobs that will last for 10 years, making the (Eurofighter) Typhoons, so really big for our country," he said.

Britain's defence ministry described the order, which would involve 20 Eurofighters, as the "biggest fighter jet deal in a generation", saying it would strengthen Turkey's combat capabilities and bolster "NATO's strength in a key region".

"This is the southeast flank of NATO, and so having that capability locked in with the United Kingdom is really important for NATO," Starmer said in the Turkish capital.

Erdogan hailed the agreement as a new symbol of defence cooperation with Britain.

"We regard this... as a new symbol of the strategic relations between our two close allies," he said after the pair signed the agreement.

But the high-profile visit was clouded by a spying scandal which erupted late on Sunday, after a Turkish court charged Istanbul's jailed opposition mayor with espionage over his links to a Turkish businessman allegedly spying for Britain.

Starmer arrived with his Defence Minister John Healey and Air Chief Marshall Harv Smyth, the head of Britain's air force, who were welcomed by their Turkish counterparts, Turkey's defence ministry said.

Turkey has been looking to modernise its air force and has been pushing to acquire 40 of the European-made fighter aircraft, which are jointly produced by Britain, Germany, Italy and Spain.

Speaking on condition of anonymity, a Turkish official told AFP Britain would hand over a number of jets on Monday, without saying how many.

Analysts said it would likely be two.

"Turkey and the Eurofighter is quite the saga," Aaron Stein, president of the Foreign Policy Research Institute, told AFP, saying Ankara had turned down an offer to join the European consortium building the jets, focusing instead on the US fighter jet programme.

"Ankara was invited to join the consortium or become an equal member a few times but they chose the F-35," he said.

After Washington booted Ankara out of its F-35 fighter programme in 2019 over its purchase of an S-400 Russian surface-to-air missile defence system, Turkey turned its attention to Europe.

- Qatari leader's visit -

Last week, Erdogan held talks in Doha with Qatar's Emir Sheikh Tamim bin Hamad Al Thani, with Turkey floating plans to acquire some of its Eurofighters.

Qatar ordered 24 Eurofighters in 2017, with the last two due to be delivered this year. It moved to acquire 12 more late last year, observers said.

Any such move would likely be part of the deal with London, which would have to grant its approval for a transfer, analysts said.

The Qatari leader is in Ankara on Tuesday for talks to clarify certain outstanding issues, the Turkish official said.

The jets Britain was to sign over to Turkey on Monday were likely to be those that had been destined for Qatar, Stein said.

Instead of being sent to Doha, "they'll simply be shipped to Turkey," he explained.

Gaza's future is also likely to feature in talks between Erdogan and Starmer, with Turkey keen to join an international stabilisation force -- an idea opposed by Israel.