Shell pipeline still leaking

London - Oil major Royal Dutch Shell said its ruptured pipeline in the North Sea continued to leak oil, although at a much slower rate, in what is thought to be the worst UK oil spill for over a decade.

"The flow line leak is reduced to less than two barrels per day," Glen Cayley, technical director of Shell’s European exploration and production activities, told BBC Radio 4 on Tuesday.

Shell's update on the leak came as criticism was levelled at the company by environmental groups for its lack of transparency. Sensitivities remain high about marine oil leaks in the aftermath of BP's massive Gulf of Mexico spill last year.

Reuters revealed on Saturday that the spill on the Gannet field, which Shell co-owns with Exxon Mobil and which lies 180 km off the Scottish port of Aberdeen, had been leaking for two days before the authorities or Shell revealed it.

Speaking in the radio interview, Cayley defended the company's initial silence saying the leak was located among complicated underwater infrastructure.

"Only when we had confident information, really, did we want to share that and since Friday we've issued daily bulletins and updates," he said.

The company was not able to give an estimate of when it expects the pipeline to stop seeping oil, a spokesperson said.

Shell said around 216 tonnes of oil, equivalent to 1 300 barrels, had leaked into the North Sea in a "significant spill", but the rate at which it was flowing had been reducing since Wednesday when a well was shut off.

Cayley said Shell was confident that oil from the leaking pipe would not reach the shore line.

"At its maximum the sheen on the surface was some 30 kilometres in length, but thanks to fairly harsh weather conditions that's now diminished," Cayley said, noting waves had helped to disperse the slick.