How might Russia target us... and will there be gas shortages? As the crisis in Ukraine deepens, we answer the vital questions over possible retaliations to the West's sanctions

 The crisis between Russia and the West has intensified following Vladimir Putin's decision to recognise breakaway republics in east Ukraine - and Joe Biden warning that the world is now on the brink of war.

A convoy of 100 tanks was seen heading toward the border as Russia prepared for a full-scale assault on Ukraine, and the parliament in Moscow endorsed the Russian president's request to deploy troops abroad.Meanwhile, Mr Putin last night supported the territorial claims of Kremlin-backed separatists in eastern Ukraine – including large areas currently held by Ukrainian forces – raising fears of all-out war.

Health Secretary Sajid Javid said the situation was now as serious as the 1962 Cuban missile crisis, and Nato secretary-general Jens Stoltenberg call it 'the most dangerous moment in European security for a generation'. 

Britain, the US and the European Union launched co-ordinated sanctions against Russian banks and oligarchs close to the Russian president - and Boris Johnson said the West should now steel itself 'for a protracted crisis'. 

As Germany suspended approval of the controversial Nord Stream 2 gas pipeline, here are answers to some of the key questions surrounding the crisis in eastern Europe: 

What is the cause of the tension in the region?

The current difficulties date back to the overthrow in 2014 of the pro-Moscow Ukrainian government of Viktor Yanukovych, prompting fears in the Kremlin that the country was moving into the orbit of the West.

President Vladimir Putin responded by sending in troops to annex Crimea while Russian-backed separatist rebels seized territory in eastern Ukraine in bloody fighting with the Ukrainian military.What has happened now?

Mr Putin has decided to recognise the two Russian-backed regions in east Ukraine - Donetsk People's Republic and Luhansk People's Republic - as independent states.

He has ordered troops into the two regions to 'maintain peace' - crossing the red line set by the West by deploying Russian forces on Ukrainian territory.

Russian President Vladimir Putin speaks at the Kremlin Grand Palace in Moscow, Russia, todayWhat has been the response?

The UK, European Union and United States will all impose economic sanctions.

Boris Johnson said the measures being imposed by the UK were the 'first barrage' because further action would be taken if the situation escalated.

So, what next?

The West will hope the economic pressure it can impose through sanctions will persuade Mr Putin to back down.

But he has an estimated 150,000 troops ringed around Ukraine and Mr Johnson warned 'all the evidence is that President Putin is indeed bent on a full-scale invasion of the Ukraine'.

An attempt to conquer Ukraine could lead to a prolonged and bloody conflict.

Russian armoured vehicles are pictured yesterday in Rostov-on-Don on the Russian side of the Ukrainian borderCould there be a wider war?

Ukraine is not a member of Nato, so the alliance's members - including the UK - will not play a direct role in fighting.

The UK has supplied anti-tank weapons to the Ukrainian army and other support is being considered.

But Russian aggression in eastern Europe is likely to increase anxiety among Nato's members.

This could lead to a further build-up of forces, potentially increasing tensions even further in the region.

What is the advice for Britons in Ukraine?

They have already been told to leave while it is still possible to do so.

The British ambassador in Ukraine Melinda Simmons has relocated from the embassy in Kyiv to Lviv in the country's west due to fears about the risk posed to the capital from an invasion.

In a message on Tuesday she said: 'I strongly advise British nationals to leave the country while commercial travel is available.' 

Financial experts have pointed out Europe's dependency on Russia for natural gas, as shown in this Associated Press graphic

Will Britain send troops to Ukraine?

Britain has provided training to Ukrainian forces since 2015 following Russia's annexation of Crimea, and has supplied them with anti-tank weapons and body armour, helmets and combat boots.

But it pulled its own troops – around 100 military personnel providing training – from Ukraine earlier this month.

The Government has signalled it intends to rely on sanctions rather than military might to enforce its message to Vladimir Putin.

But it sent more troops and equipment to Estonia – a Nato member – earlier this month amid fears that the Baltic states of Estonia, Latvia and Lithuania could come under threat.

Will Britain be hit by gas shortages?

The UK only takes about three per cent of its gas supplies from Russia, but wholesale gas prices are determined by the international market – and Europe is heavily reliant on Russia.

As other countries try to find others sources to replace Russian gas, the price will be driven up, with predictions yesterday of another £700 on to annual bills once the price cap is raised.

Some energy-intensive industries have warned they may be forced to shut down temporarily.

The price per therm in pence is shown for UK natural gas prices, which could be set to soar due to the situation in Ukraine

What about oil prices?

Motorists have been warned to expect petrol prices to rise above £1.50 per litre, as oil prices reached their highest level since 2014.

Russia is one of the world's largest producers of crude oil.

Crude oil is approaching $100 a barrel, and analysts said that could rise to $120 if supplies were restricted, which could mean petrol prices would rise to more than £1.60 per litre.

Such a rise would send inflation soaring in most Western economies.

How has the stock market reacted?

Stock markets around the world tumbled after Putin's troops announcement, but showed signs of recovery during the day.

The FTSE 100 index in London closed 11 points lower at 7,495.97.

The Centre for Economics and Business Research think tank warned that the Ukraine crisis could fuel inflation and slow down growth in the main Western economies.

Some British businesses could also be affected by sanctions against Russia, including BP, which has a significant share in the Russian energy firm Rosneft.

Any prolonged impact on the financial markets will also affect pensions, as most pension funds invest primarily in stocks and bonds.

Defence Secretary Ben Wallace (yesterday, at a meeting of the defence ministers of the Joint Expeditionary Force nations at Belvoir Castle in Leicestershire) said the UK will launch retaliatory cyber attacks on Russia if it targets Britain's networks

Will this start a refugee crisis?

Defence Secretary Ben Wallace has warned that a Russian invasion of Ukraine could lead to millions fleeing the country.

He said Europe could face its biggest internal refugee crisis since the Second World War.

Ukrainian defence minister Oleksiy Reznikov told the BBC: 'It will be a disaster not only for Ukraine, it will be a disaster for Europe.'

Officials in Whitehall and their counterparts in Europe are already drawing up contingency plans for a possible influx of one million Ukrainians fleeing into neighbouring countries such as Poland and Romania.

Tory MP Mark Pritchard, who chairs the all-party parliamentary group on Ukraine, said it was 'highly likely' the UK and EU would be affected.

He said: 'The EU needs to avoid another migration crisis. It is highly likely that the whole of the EU will be affected, the UK too, but France, Poland, Hungary and Germany are most likely to feel the biggest effect.'

Will Russia retaliate over Britain's sanctions?

Britain faces a wave of Russian cyber-attacks over its defence of Ukraine, senior military advisers have warned.

Chief of the Defence Staff Admiral Sir Tony Radakin told the Cabinet earlier this month that the UK should be ready for potential cyber offensives from the Kremlin if Russia invades Ukraine.

Officials fear that the NHS, local government and business could be prime targets for Moscow, which has one of the most sophisticated cyber capabilities in the world.

The National Cyber Security Centre (NCSC) has issued a warning to businesses and institutions to beef up their defences in anticipation of a potential Russian attack.