Prime Minister Prayut Chan-o-cha and British counterpart Theresa May shook hands in the traditional 10 Downing Street photo op as small groups welcomed and protested against the visit.
The prime minister arrived and went almost directly to his meeting with Ms May.
Prime Minister Prayut Chan-o-cha posed for the traditional photo op with Prime Minister Theresa May at her official residence of No.10 Downing Street in London. (Photo courtesy Government House)
During their conversation, Ms May called for "free and open elections".
Gen Prayut, who had previously promised elections in February, promised the British leader he would hold a general election "early next year".
Gen Prayut has said his visit is not political, and he seeks only to enhance trade and encourage European investment.
"This visit follows the resolution of the Foreign Affairs Council of the European Union that wants to upgrade relations with Thailand although this is not 100% yet," he claimed.
However that goes, he made it clear he would not be seeking extradition of fugitives including new British resident and ex-premier Yingluck Shinawatra.
After the outdoors handshake, Ms May led Gen Prayut inside her official residence, where the two sat for another photo op, and then shooed out photographers to hold bilateral talks.
Gen Prayut was met at 10 Downing Street by separate, small groups of demonstrators, about half of whom where there to welcome him to Britain and the other half to criticise.
Small groups of Thais, kept apart by British security, protested Gen Prayut's visit (above) and welcomed him. (Photos above and below FB/BBCThai)
Security forces kept the two groups well separated, and no incidents were reported.
The visit was covered by the BBC Thai service and other agencies. Government House in Bangkok quickly released photos of the meeting between Gen Prayut and Ms May.
The BBC's Thai-language site reported that Gen Prayut met with a group of Thais who welcomed him to Britain.
On Facebook, BBCThai displayed video of Gen Prayut arriving at No.10 and being greeted by Ms May.
The Facebook site also had interviews with members of the pro-regime and anti-Prayut groups at the scene.
The unstated purpose of the visits to Britain and France this week and next is to gain prestige for the military regime.
The EU was arguably the harshest critic of the May 22, 2014 coup. Gen Prayut and staff have been eager to imply that the visit to Europe shows that the European Union has accepted military-led rule in Thailand.