Johnson, girlfriend fly economy to the Caribbean

Johnson touched down in St Lucia on Thursday morning after a long-haul British Airways flight from London, the Daily Mail reported on Saturday.

In a photograph taken by a fellow passenger, the Prime Minister can be seen at a window seat reading a book while Symonds is sitting beside him.

The couple were seated in economy towards the back of the plane, where passengers can often feel more turbulence than those at the front.

A source told the Daily Mail that the couple kept a "low profile" for the duration of the flight and were accompanied by "little security".

The cost of the flight would have cost in the region of 1,323 pounds ($1,730) each, significantly less than if the Prime Minister had used a Royal Air Force private jet - which would more likely weigh in at around 100,000 pounds.

The couple were also not offered an upgrade on the flight due to strict anti-bribery and corruption rules in place at airlines.

Upon their arrival, Johnson and Symonds were received by St Lucian Prime Minister Allen Chastanet.