British holidaymakers are being warned of a possible summer of misery around cross-Channel ports after a weekend which saw thousands stranded on roads into Dover amid chaotic scenes some claimed could even be French "payback" for Brexit.

Motorists were forced to sleep in their cars for two nights in a row after a manpower crisis at French border posts triggered 20km tailbacks on the M20 and A20 roads at the weekend.

The French authorities have introduced extra security checks after recent terrorist attacks, including the Nice atrocity last weekend.

But checkpoints in Dover were left seriously undermanned despite a huge increase in traffic as the annual British holiday exodus got under way.

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MPs demanded an apology from the French Government and urged the UK Border Force to bill their French counterparts after British officials stepped in to help ease the jams.

Yesterday Xavier Bertrand, president of the Calais area regional council, condemned the queues as "unacceptable" but said they underlined how Brexit would have "consequences".

Many frustrated motorists questioned whether the mayhem may have been deliberate as a foretaste of the isolation Britain could experience if free movement is limited as part of a deal to take the UK out of the EU.

Andrew Bridgen, the Conservative MP, said he hoped it was not a "reaction to Brexit".

"Theresa May and Boris Johnson should be asking their French counterparts for an explanation for this delay."