Why it happened - questions that hold key to the crisis

Why haven't the police been able to remove the blockades?

Why haven't the police been able to remove the blockades?

Police chiefs say that in most cases there is no illegal blockade of refineries or oil terminals and that the oil companies have decided simply not leave their depots. As long as such "protests" remain peaceful and do not obstruct the highway with a physical barrier, the police say they can do little to force their removal.

The Association of Chief Police Officers pledged last night to ensure the free movement of fuel supplies, saying there was no reason why the oil companies should not move their tankers. Powers exist under the Police and Criminal Evidence Act 1994 to allow forces to arrest those obstructing roads. They can also detain individuals for threatening or abusive behaviour under the Public Order Act 1986.

Why haven't the oil companies ordered their drivers to take the petrol tankers out?

The oil companies say their legal obligations to protect the health and safety of their staff mean they cannot ask employees to break the blockades. Shell has claimed drivers at its Stanlow refinery in Cheshire have received death threats, an allegation strongly denied by protesters. Texaco has similarly pointed to an alleged incident where a missile was thrown at the windscreen of a vehicle on Sunday at its refinery in Pembrokeshire.

Sources have also admitted there is support within the oil companies for the protests and the aim of reducing the amount of fuel duty claimed by the Government.

Who is behind the protests?

An ill-defined group of militant farmers, calling itself Farmers For Action, is one of the key forces behind the demonstrations at oil installations. It was founded in the Midlands earlier this year by about a dozen farmers because of discontent with the stance of the National Farmers' Union. They have no designated leader. A looser alliance of farmers from north Wales has also played a key role in the protest at Stanlow.

Hauliers belonging to the Road Haulage Association have led a series of legal go-slow protests on main roads and in city centres. No recognised body for truckers has admitted any part in organising the illegal blockades.

What options does the Government have?

The emergency powers evoked by the Privy Council on Monday night under the Energy Act allow the authorities to compel oil companies to provide fuel for bodies including the emergency services and public transport operators.

They also allow the Government to force a general restoration of fuel deliveries and use troops to do so, although calling in the Army has been discounted so far.

The Chancellor, Gordon Brown, could also make an immediate reduction in excise duty and VAT on fuel by statutory order. Last night he ruled out any such move.

If the Government does nothing, how long will it be before Britain shuts down?

Industry experts say therewill no fuel left for sale anywhere in the country within the next 24 hours.

The resulting shortages will lead to a progressive shutdown over the next 48 to 72 hours with newspapers and other non-food items unavailable from Thursday onwards.

The major supermarkets have said they have enough food and fuel in stock to ensure supplies for another three to seven days.

If the petrol companies resume deliveries today, how long before we get back to normal?

Main petrol stations, such as those in city centres or on motorways, should have their stocks replenished within 48 hours.

Smaller outlets have been told not to expect deliveries until the middle of next week. The Petrol Retailers' Association said it would take a week for normality to return.