A trade union has threatened to disrupt the summer holidays of millions of Britons with plans to “shut down” Heathrow.

As many as 4,000 staff are planning to hold strikes on two of the airport’s busiest weekends of the year, which will lead to cancelled flights and huge queues. Ministers have called on the organisers to “think twice” before ruining people’s breaks.

The strikes, planned by Unite following a pay dispute with airport bosses, will take place on the first weekend of the holidays for most schools and across the August bank holiday weekend.

Chris Grayling, the Transport Secretary, said: “Whatever the rights and wrongs of a dispute, there can’t be any justification for actively trying to disrupt people’s summer holidays at such a busy time of year.

“I hope the unions will think twice before going ahead with these disputes and undermining people’s summer.”