Rev Michael Nazir-Ali, the former Bishop of Rochester; Anglican vicar Rev Andrew Ashdown and two crossbench peers, Baroness Cox and Lord Hylton, travelled to discuss the plight of Christians in Syria since the outbreak of the civil war in 2011.
Their meeting has been criticised by vice-president of the All Party Parliamentary Group on Syria and Labour MP John Woodcock.
Syria:
Leader: President Bashar al-Assad
Population: 18.6 million, 772,000 Christians
Main Religion: Islam
Source of Persecution: Islamic extremism
Speaking in The Telegraph, he said: "It is shocking to see British parliamentarians giving international pariah al-Assad a photo opportunity to distract from the brutal and ongoing slaughter he is perpetrating on Syrian families.
"Whatever good intentions this British delegation has will fail; their presence at this man's side can only strengthen him as his campaign of terror continues."
Britain stopped diplomatic relations with Syria after 108 civilians were massacred in May 2012.
The Foreign Office has spoken, saying British visitors "do not represent the British Government."
Premier has tried to contact the visiting party and is awaiting a response.
Syria ranks at number five on Open Doors World Watch List for persecution against Christians.
Thousands of believers have fled since the start of the civil war.
