A travel expert has issued a warning after a pair of holidaymakers were refused boarding for their connecting flight at Heathrow.

Siblings Katie and Richard were set to attend a family wedding in Thailand and booked flights with holiday agent TravelUp.

Their journey would see them head from Glasgow to Chiang Mai, connecting at Heathrow and Beijing along the way. They were flying with British Airways and Air China. 

However, things took a turn when they attempted to head from Terminal 5 to Terminal 2 in Heathrow, parent Kevin Duffy told The Times. 

TravelUp's itinerary left 90 minutes for the connection, but when the pair got to their gate they were refused boarding by Air China and notified it had closed. 

As a result, they were seen as a "no-show" and 'the remainder of the itinerary was cancelled,' Kevin explained. 

Katie and Richard had to cough up more than £4,000 for new flights after being unable to contact TravelUp.

To complicate things further, their baggage was left at Heathrow. 

In the end, Air China revealed the time given to transfer to the connecting flight by TravelUp wasn't enough and that two hours minimum should be accounted for.

Kevin also added TravelUp hasn't responded to their attempts to contact.

Julia Brookes, Travel Doctor at The Times, responded to Kevin and urged travellers changing at Heathrow to allow at least two hours for the connection to go smoothly.

She issued this warning, making sure to add passengers should leave the additional time even if the airlines say different.

Thankfully, the travel expert was able to secure a refund for Katie and Richard, revealing how TravelUp apologised for the situation. 

The agency explained that the intinerary featuring both BA and Air China with no codeshare 'may have contributed to how the connection was handled'.

What's more, TravelUp believes the route should have worked out as it only sells journeys that airlines offer themselves.

A spokesperson told The Times: 'We have been in close contact with the airline and they have confirmed that the minimum connection time at London Heathrow is 90 minutes. 

'As a gesture of goodwill, the airline has agreed to refund both tickets in full, despite the tickets originally being non-refundable. 

'Once the refund has been settled back into our account by the airline, we will process the full refund to the passengers without delay.' 

As for the additional flights Katie and Richard booked to resolve the issue at the time, Julia says they have to approach Air China for the refund. 

The Daily Mail approached TravelUp for comment.