Oil has begun to flow from a group of fields west of Shetland following a £4.4bn investment aimed at revitalising the area.

The Schiehallion and Loyal fields could produce 450 million barrels of oil over the next 20 years, according to BP's estimates.

They were first tapped in the 1990s and have already produced around 400 million barrels.

BP's multi-billion investment is aimed at extending their working lives and included the construction of the world's largest harsh water production vessel.

Chief executive Bob Dudley said: "The start of production is an important milestone for BP, marking a return to growth for our North Sea business.

"As one of the series of important, higher-margin major projects that are now steadily coming on line for BP, it also underpins our expectation for growing production and cash flows from our Upstream business over the coming few years."

In recent months, BP has announced plans to sell part of its stake in the Sullom Voe oil terminal for £68m, scrapped plans for a new power plant at Grangemouth and revealed it it will sell the UK's biggest oil pipeline for £200m.

Despite this, BP has said it intends to double its North Sea production to 200,000 barrels per day by 2020.

The price of a barrel of oil has have fluctuated heavily this year, dropping to $49 in March before rising to $54 in April, then plunging to $46 in May. It now sits at around $51.