In Parliament on Wednesday, Prime Minister Theresa May was questioned on the measures she was taking in response to the nerve agent attack in Salisbury.

Conservative MP Stephen Crabb asked: "Is she aware that Britain has recently started to receive shipments of liquefied natural gas, and does she agree that Britain should not provide a market for Russian gas? If we need to bring in extra LNG imports, we have allies such as Qatar, Malaysia and Australia who are more than willing to sell it to us."

Mrs May responded: "I can reassure my right honourable friend that in looking at our gas supplies we are indeed looking to other countries."

So how reliant is the UK on gas from Russia?

Throughout Europe, 37% of gas demand was met with Russian-sourced gas in 2017, according to energy analysts Wood Mackenzie.

However, in the UK, most of the natural gas imported comes by pipeline from Norway, the Netherlands and Belgium.

There are no pipelines that allow Russian gas to flow to the UK from Norway (the biggest source of imports).

But it's impossible to establish the source of gas flows from continental Europe coming to the UK through pipelines.

The government estimated in 2016 that Russian gas via this route would make up around 1% of the UK's gas imports.

A spokeswoman for the Department for Business, Enterprise and Industrial Strategy (BEIS) told BBC News that the UK "benefits from highly diverse and flexible sources of gas supply. We estimate less than 1% of our gas comes from Russia and are in no way reliant on it".

About a quarter of natural gas imports are shipped to the UK in the form of liquefied natural gas (LNG).

LNG is a liquid form of the ordinary natural gas we use. When it reaches its destination it is reheated, turned back into gas and distributed through pipelines to homes and businesses.

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In 2016, 92% of LNG imports came from Qatar. Russia did not appear on the list of suppliers.

But in 2018 the UK has bought some liquid natural gas from Russia.

Energy consultancy Wood Mackenzie said that this year the UK has imported three cargoes of Russian LNG from the Yamal gas project in northern Siberia.

Murray Douglas, research director at Wood Mackenzie, said: "Each cargo provides around 0.1 billion cubic metres of gas. UK gas demand so far in 2018 stands at 21.15 billion cubic metres. So, direct Russian gas imports to the UK have accounted for 1.4% of total supply so far."

A BEIS spokeswoman confirmed that Russian LNG was unloaded at the Isle of Grain terminal near Kent, and at the Dragon LNG terminal in south Wales.

Consultancy firm McKinsey has said that the closure of the Rough gas storage facility in the North Sea means that the UK is more reliant on gas imports from overseas.

In the early part of this decade, the UK's reliance on imported energy had an upward trend, according to the ONS, but then started falling. Net imports accounted for 36% of energy use in the UK in 2016, down from a peak of 48% in 2013,

Image copyright Reuters

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