"The plane got as far as Ireland and then they found out the first officer was still in training.
"The qualified first officer, who was flying alongside an experienced captain, was replaced with a new pilot to ensure full compliance with Virgin Atlantic's training protocols, which exceed industry standards.
"We apologise for any inconvenience caused to our customers who arrived two hours, 40 minutes later than scheduled as a result of the crew change."
A UK Civil Aviation Authority spokesperson said it was made aware of the incident by the airline and confirmed "both pilots were suitably licensed and qualified to undertake the flight".
The captain has been described as "highly experienced" with "many thousands of hours of flight time during 17 years at Virgin Atlantic", while his co-pilot was said to have joined the airline in 2017.
Virgin Atlantic, which is largely owned by billionaire Richard Branson, blamed the incident on a "rostering error".