Esso has tightened security on its network of underground pipelines after two attacks on its Midline pipeline during April.

In a statement the company said: “Our pipeline network has been in place for decades and tapping incidents are rare. We have security and detection measures in place at all company facilities, including our petroleum product pipelines, and we work closely with the police to detect and close down illegal activity relating to our assets.

“Recent instances on Midline have prompted Esso to strengthen our security and monitoring procedures. This approach is proving effective at identifying such illegal and highly dangerous activity. We do not respond to questions that relate to our specific security measures or detailed incidents for obvious reasons.”

In the first incident, discovered on April 2, thieves had dug down to the pipeline near Manton in Wiltshire and placed a tap. However, a farmer ploughing his field cut through a pipe the thieves had attached to the tap and a quantity of fuel leaked out.

Police and seven fire appliances attended over a 32-hour period as a result of the leak and the pipeline had to be closed down while it was repaired. Esso is currently working with the environment Agency to assess the impact of the leak.

In the second incident, the pipeline was shut down after a tapping device was found inserted into it in Hampshire on April 18, and it resumed operation a week later following repairs and tests.

The device in the pipeline was discovered near an industrial storage unit at West Wellow, Romsey, where 30,000 litres of diesel, believed to have been stolen from the pipeline, were recovered.

Hampshire police said two men, both from the Salisbury area, were arrested on suspicion of conspiracy to steal fuel, and have been bailed until July 10, pending further enquiries.

The Midline pipeline carries fuel from the Fawley Refinery on the south coast to the Birmingham Fuels Terminal.