Plane passengers warned 'secret boarding pass code' could see you kicked off flight

UK airports are gearing up for a record summer travel boom, with millions of us planning to fly to exotic destinations. But with budgets getting ever tighter, airlines are even more likely to deliberately overbook flights to eliminate any risk of wastage due to passengers failing to show up for their booked flights.

But with that deliberate overbooking comes the risk of being turned away at check-in.

How can travellers work out if they're at risk of missing out on their flight? Experts from leading luxury airport transfer provider SCS Chauffeurs explain that there's a unique code on every boarding pass.

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According to the UK Civil Aviation Authority, more than six million passengers were denied boarding globally in the last year, with many unaware that early check-in could have guaranteed their flight.

Hadleigh Diamond, luxury airport chauffeur provider at SCS Chauffeurs, explains: "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, which is increasingly common during peak periods – airlines have to choose who gets involuntarily denied boarding."

One of the main factors used is the check in order. If you were one of the last to check in, you're more likely to be 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 it the moment it opens.

Secondly, if you're flying with friends or family, make sure everyone checks in together to avoid getting split up by the SEQ system. In worst-case scenarios, some members may board while others are denied.