The fate of up to 13 ageing US warships destined for the UK for recycling hangs in the balance. These are the key issues.
What is the controversy about?
The first of the contaminated former US warships due to be dismantled at a UK yard are being stored on Teesside pending a decision on their future.
The yard's owner, Able UK, has a $16m (£10m) contract to break up the vessels, but has run into problems over planning consent and waste-management licences.
Campaigners fearing major environmental implications persuaded the High Court to prevent any work until regulators had decided whether to grant permission.
What are the principal dangers?
The ships are up to 60 years old and are said to be fragile and at risk of breaking up, sparking pollution fears.
They contain a range of toxic materials, including lead, mercury, asbestos and polychlorinated biphenyls (PCBs), which have been linked to cancer and other health conditions.
Conservationists fear nearby wildlife sites are threatened by possible leaks.
But the Environment Agency says risks are low - if the facilities are safe.
Why is US toxic waste coming to the UK?
An American subsidiary of Able UK won the contract to recycle 13 of the obsolete ships, and chose to carry out the work at Able's Hartlepool shipyard.
Environmental campaigners say the US has the technology to do the work.
But the UK's Environment Agency initially agreed to the transfer on the basis that all approvals were in place.
It subsequently transpired they were not - so new consents must be sought.
Why were the ships allowed to be moved?
The Environment Agency, which regulates waste shipments and treatment in England and Wales, approved licence amendments.
But subsequent investigations showed that planning permission for a dry dock and waste-management documents on which it based its decision were not valid.
By the time the true situation was established, the first four ships were on their way. The government agreed to allow them to dock, but no work can be done until and unless various consents are granted.
So what happens now?
Able UK must apply again for permission to build a dry dock at its base near Hartlepool to carry out the dismantling.
It also needs to apply for a new waste-management licence. Both applications will require assessments of their impact on the environment.
In the meantime, a government select committee is investigating how the ships were allowed to leave for the UK without the requisite permissions.
And the EU plans to tighten its own laws on importing and exporting ships for decommissioning.
Oils and oily ballast water could cause damage to the marine environment.
Asbestos is a known carcinogen but is denser than water and non-soluble so would only pose a problem if blown on shore.
PCBs have been called a "probable carcinogen" and have been linked with neurological and developmental problems in humans.
Mercury, lead, chromium and cadmium are highly toxic metals which accumulate in the body.