The Prime Minister has saved British taxpayers tens of thousands by flying economy class for his Caribbean holiday with girlfriend Carrie Symonds.    

 touched down in St Lucia on Thursday morning after a long-haul flight from London.

In a photograph taken by a fellow passenger, the Prime Minister was seen at a window seat reading a book while Ms Symonds snuggled underneath her coat.

The pair appear to be seated in economy towards the back of the plane, where passengers can often feel more turbulence than those at the front.

A source told MailOnline 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 £1323 each, significantly less than if the Prime Minister had used an RAF private jet - which would more likely weigh in at around £100,000.

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

But Mr Johnson and Ms Symonds appeared happy to do their bit and save the taxpayer money ahead of their break in Mustique - their final destination - where they are staying in a luxury villa.

Ms Symonds earlier this month proved herself a thrifty character after it was revealed she hired her designer outfits, rather than buying them outright.

It also burnished her green credentials, in keeping with her day job as an adviser to environmental campaign group Oceana. 

Ecstatic British Airway crew squeezed around Mr Johnson and his St Lucian counterpart Allen Chastanet for a picture on the steps of the airplane after it touched down on Boxing Day. 

Mr Johnson also mustered a thumbs up as he wrapped an arm around Mr Chastanet, who congratulated him on his thumping election victory. 

Mr Chastanet said on Thursday: 'Today we welcomed British PM Boris Johnson to Saint Lucia for a short layover.

'I thanked the PM for his country's continued support to our country and the region and of course took the opportunity to once again offer my heartiest congratulations on his hard-won and well-deserved victory in the recent election.

'We look forward to working more closely together on our countries' shared mutual interests.' 

With a bag slung over his shoulder, the PM emerged from the plane wearing a dark suit jacket and trousers to meet the St Lucia leader.

But he is expected to leave all formal government duties at the door of his £20,000-a-week Caribbean villa where he and 31-year-old girlfriend will toast in the New Year and celebrate keeping the keys to Number 10. 

Compiled by Olalekan Adeleye

MailOnline