The environmental group is convinced there is enough evidence to launch a criminal prosecution for the pollution caused after the tanker ran aground at the entrance to Milford Haven harbour a year ago today.
But it is not yet sure who to prosecute; yesterday its campaigns director Tony Juniper said the Department of Transport, the Milford Haven Port Authority and the tanker's managers, Acomarit UK, were all possible candidates.
Leigh, Day & Co, lawyers for Friends of the Earth, have written to the Environment Agency to say that unless it initiates a criminal prosecution by 15 April the group will launch a private one.
The letter complains that the agency, which has strong powers to prosecute water polluters, has had nearly a year to consider prosecuting - but has still not yet decided whether to do so. The agency confirmed yesterday that its own investigations are continuing.
"What's going on?" asked Mr Juniper. "It's clear that this disaster was avoidable. If justice is to be done, then we must have proper enforcement of environmental law."
Yesterday Friends reinforced its point by dumping several pails of Sea Empress oil on the steps of the Department of Transport in Marsham Street, central London. The pollution can still be found from time to time on Pembrokeshire beaches because it is lifted out of remote coves or off the seabed during storms and at high tides.
The fully laden tanker struck rocks then lost a small quantity of its cargo of North Sea crude as it entered Milford Haven in south-west Wales, on 15 February last year.
But over 70,000 tonnes, much more than half its cargo, was lost during the many attempts to salvage the ship over the next week. Tugs failed to hold the tanker in place as strong tidal currents dragged it over the rocks, holing it again and again.
Eventually it was refloated and brought into port. The ship has now been repaired and is going back into service. But Pembrokeshire suffered Britain's most damaging oil spill since the Torrey Canyon struck rocks off Cornwall 30 years ago.
The Government's official accident investigation report will not be published for about another month. This has examined the initial grounding and the salvage operation carried out jointly between the Coastguard Agency's Marine Pollution Control Unit and the port authority, and widely regarded as having been bungled.
The Marine Conservation Society said that despite the recommendations of the Braer inquiry by Lord Donaldson, there was still no permanent fleet of salvage tugs stationed around the UK to be called on in tanker emergencies. The DoT maintains three very powerful "supertugs" - one near Dover, Kent, one off the West Country and one near the Hebrides - in the winter only.
Environmental groups and local people were furious that there was no public inquiry into the disaster, even though it happened just three years after Britain's previous big oil spill. In 1993 the tanker Braer lost all power, struck the Shetland isles and spilt all its cargo. Far less damage was caused along the Shetland coast than in Pembrokeshire because raging storms dispersed the oil.
But the Sea Empress oil washed onto 120 miles of cliff and beach, much of it in Britain's only maritime national park. Five thousand sea birds were known to have been killed, but many more died because the bodies of most oiled seabirds never reach the shore.
There was a ban on all fishing in surrounding waters, but that has been progressively lifted. The harvesting of shellfish is still not allowed from between the low and high tide marks and a couple of small sea areas. Nor can edible seaweeds and samphire be harvested.
Nearly pounds 2m is being spent on around 100 scientific studies into the impacts of the spill, most of which are not yet complete. It is known that there was massive short term damage to wildlife and the breeding of some seabirds was set back. Fortunately the long term damage appears, so far, to be minor.