Now the HTA says the same GM orange petunia plants and seeds have been found in the UK. Petunias are one of Britain's most popular plants and the planting season begins in May.
GM flowering plants are banned in the EU.
The HTA has alerted the Government that the bedding plants are in the UK supply chain. Any plants or seeds found will be destroyed.
Orange petunias have to be GM-bred as they do not occur naturally. Researchers think the orange colour may have come from a maize gene.
Evira said one lot of petunia seeds (African Sunset) as well as eight petunia varieties that had already been planted were found to be genetically modified: Pegasus Orange Morn, Pegasus Orange, Pegasus Table Orange, Potunia Plus Papay, Go!Tunia Orange, Bonnie Orange, Sanguna Patio Salmon and Sanguna Salmon.
The cuttings and seeds of the GM petunias had been imported to Finland from Germany and the Netherlands. Investigations are ongoing in EU member states to establish if GM petunia plants have been placed more widely on the market.
"Every effort is being made to trace the plants so they can be withdrawn from sale," the HTA said. "We do not know how widespread they are in the UK supply chain."
The HTA added that the plants "pose no threat to people animals or the environment". The trade association says they will not survive the British winter.
EU states are trying to find out the spread and origin of the plants and seeds. European auction houses have stopped selling the plants.
African Sunset is available from many UK suppliers, as are some of the other varieties Evira has identified.
Evira said: "A specific authorisation procedure is required before genetically modified plants are allowed to be cultivated and marketed in the EU. No application has been submitted for authorisation of genetically modified petunias in the EU and they have not been authorised to be imported, cultivated or marketed in any of the member states.
"Only one genetically modified maize variety is authorised for cultivation in the EU. Some GM blue carnation varieties have been authorised for use as a cut flower only in the EU, but may not be cultivated in the EU countries. Genetically modified maize, soy and rape with EU authorisation may be imported into the EU for use in feed and food.
"All genetically modified products shall be labelled with indications of genetic engineering to enable the consumer to identify the products."