Travel disruption caused by the latest Border Force strike on Budget day tomorrow (Wednesday) is likely to be compounded by walkouts and protests by workers in France.
Travellers arriving on the UK on March 15 and early the following day have been warned to be prepared to face longer wait times at UK border control and check with their operator before they travel.
The latest caution issued by the Home Office came on the eve of strike action by the Public and Commercial Services (PCS) union which represents Border Force officials.
Several unions in France have have also called for strikes and demonstrations on Wednesday.
France has been hit by a series of nationwide strikes by workers opposing plans to raise the pension age in the country.
“This industrial action may lead to additional disruption to services and queues at French ports not due to Border Force strike action,” the Home Office warned.
Border Force chief operating officer Steve Dann said: “It is disappointing that yet again strike action may cause disruption to travellers entering the UK.
“Border Force’s number one priority to is keep our citizens safe and borders secure.
“We are working closely with port operators and partners across the travel industry to meet critical demand and support the flow of passengers and goods through our border.”
But he added: “During this period of industrial action, travellers should be prepared for disruption.
“We encourage everyone to check the latest advice from operators before travelling.”
The Home Office insisted that hundreds of people from across government and the military have been trained to carry out essential checks at the border since strikes were announced by the PCS Union.
It added: “Border Force has been working closely with port operators and carriers to ensure we have robust plans in place to minimise any delays to travellers and goods entering the UK if strike action goes ahead.”
The PCS is one of nine unions targeting a day of “all-out action” to coincide with the Budget with rallies planned for London, Glasgow, Edinburgh, Cardiff, Bristol and Aberystwyth.
Strikes in France since Saturday have led to Eurostar having to cancel a handful of services.