Shell was battling an oil leak in a North Sea pipeline off the British coast Saturday, the Anglo-Dutch oil giant company said. The leak was discovered Wednesday after an oil sheen was spotted on the surface near the Gannet Alpha production platform, 112 miles (180 kilometres) east of Aberdeen, on the Scottish east coast. A clean-up vessel and spotter plane have been sent to the scene. Shell said it was not immediately clear how much oil had spilt into the sea. \"We can confirm we are managing an oil leak in a flow line that serves the Shell-operated Gannet Alpha platform,\" a Shell spokesman said. \"We deployed a remote-operated vehicle to check for a subsea leak after a light sheen was noticed in the area. \"We have stemmed the leak significantly and we are taking further measures to isolate it. The subsea well has been shut in, and the flow line is being de-pressurised.\" Shell said their focus was on environmental safety and they had informed the relevant British authorities. A spokesman for Britain\'s Department of Energy and Climate Change said: \"We are responding to the incident and will investigate in accordance with our investigations policy. \"We understand from Shell that there is a finite amount of oil that can be released.\" The field is co-owned by Esso, a subsidiary of US oil firm Exxon, but is operated by Shell. A spokeswoman for the devolved Scottish government said Marine Scotland, the body wich manages Scotland\'s waters, was in close contact with key organisations involved, including Shell. \"We will continue to monitor the situation and update ministers,\" she said. North Sea oil production is a major industry in Scotland, centred on Aberdeen. As Britain battles to rein in its record deficit and revive growth, it is a key sector being relied upon by the Treasury. In March, Britain raised the rate of tax on companies operating in the North Sea to enable lower petrol prices for motorists hit by soaring oil costs. The charge levied on oil and gas production went up from 20 percent to 32 percent. Finance minister George Osborne said the move would raise an additional £2 billion ($3.3 billion, 2.3 billion euros) for the state coffers. Scotland\'s Green Party co-leader Patrick Harvie said it was imperative that Shell act \"urgently and efficiently\" in light of the Gulf of Mexico oil spill. \"They must also keep the public and the authorities properly informed about progress, something BP failed to do during the Gulf of Mexico disaster last year,\" he said. \"Whatever the outcome of this incident, it certainly underlines the need for the oil industry to publish proper response plans. \"If they refuse to do so, ministers should act to make it a condition of their licences.\"