UK airports are bracing themselves for a record summer travel surge, with millions of Britons planning getaways to far-flung destinations.

However, with everybody's budgets becoming increasingly stretched, airlines are more inclined than ever to deliberately overbook flights to mitigate any losses from no-show passengers. This intentional overbooking strategy brings with it the danger of being refused entry at check-in.

How can holidaymakers determine whether they're at risk of losing their seat? Aviation specialists from premier luxury airport transfer company SCS Chauffeurs have revealed that there's a distinctive code printed on every boarding pass that can predict whether you're at risk of being 'bumped.'

Data from the UK Civil Aviation Authority shows that over six million passengers were refused boarding worldwide in the past year, with many oblivious to the fact that prompt check-in could have secured their journey.

Hadleigh Diamond, luxury airport chauffeur specialist at SCS Chauffeurs, reveals: "SEQ stands for Sequence Number, and it tells airlines the order in which you checked in for your flight.

"A SEQ of 001 means you were the first to check in; 152 means you were the 152nd. While it doesn't affect your seat assignment or boarding group, it's crucial during overbooked flights, especially on budget airlines."

"When flights are oversold," Hadleigh adds, "which is increasingly common during peak periods – airlines have to choose who gets involuntarily denied boarding.

"One of the primary factors utilised is the check-in sequence. If you were amongst the final passengers to check in, you're more likely to find yourself at the bottom of the priority list.

"When we arrange transfers, we often remind passengers to ensure they've checked in early, whenever possible, to avoid a potential flight issue."

Hadleigh adds: "Airlines tend to overbook flights as not all passengers turn up on the day."

When a flight is so overbooked that passengers are denied boarding or offloaded, the airline will usually ask for volunteers.

But if no-one comes forward, each airline will deny boarding to passengers in line with its own policies: "For many airlines, this involves using the SEQ number as a fair tie-breaker.

"You might be more likely to be denied boarding if you're travelling alone or without luggage, have paid the lowest fare or were the last to check-in."

Don't assume a booked seat means that you have a guaranteed flight. Overbooking affects all classes, including economy with assigned seating.

Look for SEQ on your boarding pass – It's usually printed under or near the barcode.

A low number is better.

There are two key tips for avoiding disappointment. First of all, the experts say, try to check in as early as possible.

Most airlines allow online check-in 24–48 hours before departure. Set a reminder and check in online the moment it opens.

Secondly, if you're flying with friends or family, ensure everyone checks in together to avoid being separated by the SEQ system.

In the worst-case scenarios, some members may be allowed to board while others are denied.