Jack Cunningham, the Agriculture Minister, said he had ordered an "immediate" end to operations at the two plants following investigations by ministry officials and the European Commission's anti-fraud unit.
The announcement came on the eve of Mr Cunningham's visit to the European Parliament in Strasbourg where he will address a special committee on bovine spongiform encephalopathy (BSE) and explain the measures being taken by the Government to prevent the illegal export of British beef.
"Evidence is coming to light that some UK-based companies may have been exporting UK beef," he said. "We have uncovered very poor hygiene standards, meat which isn't properly labelled, meat which has apparently been labelled with documents from other countries and a whole number of other completely unsatisfactory activities.
"Operations of this kind involve risks to the public and I am determined to crack down hard on anyone who runs risks with public safety."
The closures follow threats from the European Commission to take legal action against Britain amid allegations of beef smuggling. The commission said it believed as much as 1,600 tonnes of British beef had been illegally imported into the Netherlands under a Belgian label of origin. Some of it was seized by Dutch officials, while other consignments were believed to have reached markets in Russia and Egypt.
The beef was apparently seized in May, but details of the discovery were suppressed during a police follow-up investigation in the UK, the Netherlands and Belgium.
Details only emerged after information was leaked to members of the European Parliament, the Commission said. Officials from the Ministry of Agriculture, Fisheries and Food said the closures were as a result of those investigations. A spokesman said few details were being released, as the inquiry was still going on.
"We have been working on this for a number of weeks and action has been taken as soon as possible to prevent any further activities taking place," he said. "The investigation is continuing."
The Commission said its veterinary inspectors had uncovered evidence which "confirmed suspicions" of an exports fraud and accused Britain of failing to police the ban effectively. There have also been claims of British soldiers being involved in smuggling beef from Northern Ireland to the Continent. British officials admitted making only occasional checks on lorries leaving Britain but said 14,000 checks had been made at ports since the ban was imposed.
The Meat and Livestock Commission welcomed the minister's tough stance as an indication of the industry's and ministers' determination to ensure high standards. However, the development will spark fears among beef farmers that returning consumer confidence in British beef could be undermined.Reuse content