The leaders of the Labour and Liberal Democrat parliamentary parties have met Hamas leader Ismail Haniyah during a visit to Gaza.
Parliamentary Labour Party chair Tony Lloyd MP and Liberal Democrat Parliamentary Party chair Lorely Burt MP met Hamas officials on Sunday.
The pair were part of a delegation of 12 British parliamentarians, including one Green Party MEP and a number of Scottish MPs and MSPs.
The British government refuses to engage with Hamas until it renounces violence, recognises Israel's right to exist and abides by previous Israeli-Palestinian agreements.
Mr Haniyeh, Prime Minister of Gaza's Hamas government, handed the visiting group a letter to be delivered to European parliaments demanding more be done to lift the siege of Gaza.
The parliamentarians entered Gaza via the Rafah crossing and returned home on Wednesday.
Their visit was funded by the Council for European Palestinian Relations, a pro-Palestinian group based in Belgium.
As well as meeting Hamas, they travelled to a water plant and spoke to representatives of women's groups.
During the trip Mr Lloyd told the Iranian-funded Press TV: "What we can do is talk to a lot of people, listen to what the problems are that people are facing, and then take that message to the world and say 'things have to change'."
Lib Dem peer Baroness Falkner was also part of the delegation. She said: "We decided it was important to meet Mr Haniyeh, given that there has been a reconciliation agreement signed between Hamas and Fatah which has been broadly welcomed internationally, and we wished to hear for ourselves whether it was going to be implemented in full."
But Labour Friends of Israel director Jennifer Gerber said the trip was "shocking".
"Just days after the visit, the Hamas regime in Gaza executed two Palestinians accused of 'collaborating' with Israel. This is not the sort of regime that it should be acceptable for a representative of a progressive party to show any solidarity with," she said.
Matthew Harris, Liberal Democrat Friends of Israel vice-chair, said: "LDFI strongly agrees with the coalition government's clearly stated policy of not engaging with Hamas, due to the actions that Hamas has taken."
A Labour Party spokeswoman said: "Labour supports UK policy not to speak to Hamas. MPs' visits arranged privately are a matter for them to comment on as individuals."