Encouraging more cruise ships to the Isle of Man could have a serious environmental impact on the island, according to ’green’ campaigners Friends of the Earth.

Group spokesman Pete Christian voiced concerns about ships’ emissions and sewage discharges and the impact of transporting large numbers of tourists around the island.

’Whilst land transport is reducing emissions, the cruise industry, building bigger craft, is going the opposite way. With huge disparity between cruise lines over sewage treatment, water quality, air pollution and environmental policy transparency, no one could identify acceptable, sustainable cruise ships,’ he said.

But a government statement said: ’Cruise ships are regulated under international conventions which have been extended to the Isle of Man. The International Convention for the Prevention of Pollution from Ships (known as MARPOL) applies to all ships and has specific and stringent requirements governing issues such as sewage, rubbish and marine fuel.’

The convention precludes any dumping of rubbish over the side into the sea and requires all ports to have facilities to deal with disposal of rubbish from ships. In addition, sewage discharge into coastal waters is forbidden and all ships must have facilities to process it.

The government insists many recent changes have been designed to reduce levels of nitrous oxide, sulphur oxide and CO2 produced from ships. It points out the sulphur content of marine fuel used in the Irish Sea has already been reduced from a maximum of 4.5 per cent to 3.5 per cent and this will reduce further to 0.5 per cent in January 2020.

But Mr Christian is unmoved by the argument: ’Cruise ships burn dirty fuel. From 2020 sulphur content must reduce to 0.5 per cent, still many times more than Euro 6 standards for cars. Low sulphur fuel still emits huge amounts of nitrogen dioxide,particulates and greenhouse gases.’

The need to run ship’s engines to power generators, even when berthed, would add to pollution, he said, and under MARPOL, broken down, disinfected sewage could be discharged only three miles from the shore.

Visiting ships are subject to Port State Control inspections to ensure they comply with regulations.

A government-commissioned report by Deloitte on the viability of a cruise ship berth for the island is currently being considered.