If you're wondering why the tanker drivers want to strike in the first place, here's a brief summary.

Oil companies outsource petrol distribution to contractors rather than do it in-house.

Retailers including the big supermarkets use these contractors to supply their petrol stations.

The contractors compete for outsourcing deals that come up for renewal every three to five years.

Drivers say their terms and conditions of employment change every time the contracts are renewed and standards, on training, health and safety and working conditions are being squeezed.

They want common minimum standards on training, health and safety and working conditions but they say the companies - there are seven - are opposed to any industry-wide standard.

Unite, the drivers' union, has been running its Enough is Enough campaign for almost a year. Read more about it here.

Drivers were balloted over strike action last week. They have until April 23 to call a strike but they are required to give seven days notice.