Prime Minister Boris Johnson has pledged to raise human rights when he meets Gulf leaders for talks about ending reliance on Russian oil and gas after the invasion of Ukraine.
He will discuss energy security and other issues in Saudi Arabia and the United Arab Emirates on Wednesday.
He said a global coalition was needed "to deal with the new reality we face".
But critics have expressed concerns about the human rights records of the countries.
Last weekend, Saudi Arabia carried out a mass execution of 81 men in one day, and its Crown Prince Mohammed bin Salman has been implicated in the murder of Washington Post journalist Jamal Khashoggi in 2018.
Labour leader Sir Keir Starmer said "going cap in hand from dictator to dictator is not an energy strategy".
Shadow climate secretary Ed Miliband the trip was "a sign of our vulnerability and energy insecurity as a country".
Ahead of the trip, some MPs had called on the prime minister to cancel his visit.
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