"This is an historic time as we have European members of parliament going to Gaza to draw international attention to Israel's collective punishment of 1.5 million Palestinians," Lord Nazir Ahmad, a Labour member of Britain's House of Lords and head of the delegation, said.
He described the Gaza Strip as the "largest prison in the world".
The politicians planned to visit local hospitals, delivering one tonne of medicines and three scanners for use in treating spinal injuries.
"The whole of the EU is colluding to what is taking place in Gaza to our shame"
former British international development minister
"We are taking very basic medical supplies like paracetamol and painkillers. We were shocked when we got the list from the Health Ministry in Gaza, it means they don't have anything," Arafat Shoukri, a UK-based doctor, said.
The International Committee of the Red Cross says virtually no medical supplies have been reaching Gaza, a situation it says ist at least partly caused by a lack of co-operation between Hamas and the West Bank-based government of Abbas.
It has also urged Israel to facilitate timely deliveries of medical supplies and equipment.
The politicians were also expected to meet some of the 700 Palestinian students who have been accepted at international universities, but have not been allowed to leave the territory.EU 'collusion'
Clare Short, a British former minister for international development, said: "We want to witness the living conditions of these people, challenge the siege, and challenge the failure of our governments to uphold the Geneva convention.
"We were not allowed through the Rafah crossing so we are going by boat because it is the only way to get in," she said.
"The whole of the EU is colluding to what is taking place in Gaza to our shame."
Several rockets were fired into Israel from the Gaza Strip into Israel on Friday in response to earlier operations by the Irseali military.
Air raids, ground raids and missile attacks this week were the first such operations since a truce was agreed in June.