Ferry passengers travelling between Britain and the Republic of Ireland now need to show a valid passport before boarding.

Previously, passengers were not always asked to show a passport but had sometimes been required to have another form of photo ID.

The changes will affect about two and a half million passengers, including car and lorry drivers sailing from Holyhead, Fishguard and Pembroke Dock.

Ferry companies Stena and Irish Ferries say they are making the change from Monday to help them comply with UK government rules on passenger lists.

One tour operator said he had already received cancellations because of the ferry operators' new policy.

The changes mean that passports will now be required to board the ferry, rather than to enter the country people are travelling to.

The website of one operator – Stena Line – says that passengers who have forgotten their passport, or do not have one, will not be allowed to board.

The company said it was "making this change to meet the requirements of the UK Border Force in relation to the accuracy and integrity of passenger data before boarding".

Border Force said the change was the ferry operators' decision.

Elfyn Thomas, who organizes bus trips between Wales and Ireland, said that some of his customers had already decided not to travel because they do not have a passport.

He told BBC Radio Cymru's Dros Brecwast: "What's been unfair to travellers is that these new guidelines were published a month ago, and they should have been published three or six months ago to give people the chance to get a passport.

"Some of our customers have pulled out of trips because they didn't have a passport, including older people who don't travel often - that's going to be a loss for us and other companies."

He added that two of his customers were currently in Ireland without a passport and will see what happens to them when they try to return to Wales.

Holyhead is Britain's second biggest ferry port, with several departures a day to Dublin.

The change also applies to other ferry routes between Wales and Ireland, from Fishguard and Pembroke Dock to Rosslare.