P&O Ferries suspended passenger services on the Dover-Calais route over the Easter bank holiday weekend, causing further disruptions for UK travellers.
The Pride of Kent and the Spirit of Britain are being held by theMCA because of safety concerns, causing ferry shortages on a key route.
The company said on its website that it was cancelling all Channel crossings over the Easter weekend.
It adds to the travel chaos in the UK, where staff shortfalls have led to flight cancellation and long waits at airports. Network Rail is carrying out 530 engineering upgrades on the west coast mainline from London to Milton Keynes and has warned passengers of delays.
Over the weekend, the AA estimates 28.6m car journeys will take place. Motorists are advised to travel on Thursday or early on Saturday to give themselves the best chance of avoiding long lines.
Edmund King, the AA president, said that Good Friday will be the busiest day for Easter trips and staycations. Some drivers may miss some jams if they leave on Thursday or early Saturday.
The Department of Transport urged people to plan ahead and allow extra time for travel, but long lines were already forming near the port of Dover on Thursday. Robert Courts said his department was working closely with operators to minimize disruption.
The two vessels were not released until the agency was satisfied that they could fulfill the requirement of the Port State Control regime.
The Pride of Kent was taken into custody on March 28th after a failed inspection by the agency.
The Spirit of Britain was taken into custody this week, compounding troubles for the firm, which is under fire for replacing all 800 of its UK workforce with cheaper foreign agency workers in March.