Twelve Britons have been held in Israel while making an attempt to visit the West Bank town of Bethlehem, according to campaigners.
The Scottish Palestine Solidarity Campaign, which organised the visit, said the specific charges were unclear.
About 700 pro-Palestinian activists from around the world had intended to visit Bethlehem.
The Foreign Office said it had received reports of Britons being detained at an airport in Tel Aviv.
The Scottish Palestine Solidarity Campaign, which had been co-ordinating the British arm of the visit, said its chairman Mick Napier, 64, a university teacher, was amongst four of its members arrested at Israel's Ben Gurion Airport on Friday.
Five English and three Welsh people were also on the flight.
Sofiah Macleod, the UK-based representative for the campaign, said she spoke to consular staff who told her the arrests had been "quite rough".
She said: "They were all handcuffed and shackled and put into vans after standing around for quite a long time, and you can see from their ages that a lot of them are retired.
"Otherwise they're all fine."
The Scottish people arrested included; Frank Thomas, 66, a retired statistician from Edinburgh; Ian Stewart-Hargreaves, who lives on Isle of Lewis; and Joy Cherkaoui, a community worker from Dumfries and Galloway.
The English plane passengers included John Lynes, 83, a retired university lecturer from East Sussex; Audrey Gray, 77, a retired nurse from West Chiltington, West Sussex, and Val Kitchen, 68, from Tonbridge.
Anne Gray, 66, a retired academic from London and Les Levidow, 61, an Open University research fellow who works in Milton Keynes, were the other English passengers.
Pippa Bartolotti, 57, deputy leader of the Wales Green Party; Dee Murphy, 56, from Swansea, founder member of Swansea Palestine Community Link; and Joyce Giblin were the three Welsh passengers.
Fiona Williams has also been identified as British, however her precise nationality is currently unknown.
"We have received reports of a number of British nationals being detained at the airport in Tel Aviv," said a Foreign Office spokeswoman.
"We have a consular team at the airport who are seeking access to them to ensure that we can provide the appropriate assistance," she said.
In recent days, airlines with flights from France, Germany and Switzerland prevented ticket-holders from boarding planes after being notified by Israel that they would be refused entry.
Palestinian civil society organisations who make up the Welcome to Palestine campaign group expected 600 to 1,000 foreign activists to take up their invitation to head to the West Bank for a week.
They say they have planned a full itinerary of peaceful activities, starting with events in Bethlehem and Ramallah on Saturday for those able to make it there.
Palestinians have no airport of their own and Israel controls the borders of the occupied West Bank.
Ben Gurion airport increased security in recent days with hundreds of extra police officers deployed to prevent any demonstrations from taking place.