The UK faces legal action in the European Court of Justice if it fails to take tougher action to prevent dolphin deaths, an MEP has warned.
Conservationists blame dolphins deaths on fishing
Conservative Struan Stevenson spoke after 21 dolphins were washed up dead in the South West in less than a week.
Environmental groups believe most of the mammals were killed after getting entangled in fishing nets.
The European Commission (EC) last year warned the government about alleged infringement of the Habitats Directive.
Fisheries spokesman Struan Stevenson said the government now "almost certainly" faced referral to the European Court of Justice following the discovery of the dolphins and the death of a whale which swam up the Thames last week.
He said that a ban on pair trawling within 12 miles (19km) of the coast, introduced in 2004, did not go far enough.
Conservationists blame pair trawlers, which hang long nets between two boats, for many dolphin deaths.
Mr Stevenson called for a no-fishing conservation zone and "comprehensive surveillance" to protect dolphins.
He said: "The tragic death of this bottlenose whale, together with the ongoing massacre of dolphins in the English Channel and off the coast of South West England, will almost certainly lead to a referral to the European Court of Justice."
A spokeswoman for the Department of Environment, Food and Rural Affairs (Defra), said: "The UK is committed to protecting endangered species such as cetaceans.
"The UK has devoted a great deal of time and effort in tackling the problem of cetacean by-catch and preservation of endangered species such as the whale."
It declined to comment on EC action over alleged breaches of the Habitats Directive other than saying: "Infraction proceedings are sub-judice and confidential between the EC and member states."