The AIM-listed company has developed a product, d2W, which uses oxo-biodegradable technology that it claims can degrade in the presence of oxygen within two years.
Critics say it just breaks down into a smaller form of plastic rather than degrading completely.
In a statement today, Michael Laurier, Symphony’s chief executive, rebutted the claims made in a BBC News programme.
“Whilst the BBC's coverage did not, in our opinion, fairly present the scientifically proven benefit of oxo-biodegradable technology, we are pleased that the BBC has now focused on the solution, and introduced our company and our d2w technology to a much wider audience."
He says d2W degrades in the same way as a leaf in the open environment.
“Symphony's d2w technology was invented to accelerate the degradation process and reduce the dwell-time of plastic in the environment, by adding a catalyst which promotes oxidation and converts the plastic into biodegradable materials.
“It is essential to understand that it does not just create fragments.“
Adding it was legitimate for the BBC to ask if d2W actually works, Laurier said it has been carrying out tests for 20 years to prove its effectiveness.
“Based on this evidence a d2w plastic product will become biodegradable if exposed to oxygen on land or sea much more quickly than ordinary plastic.”
A number of countries in the Middle East and Africa are looking at legislating for oxo- to replace existing plastics, but the European Union is under pressure to ban the substance.
Saudi Arabia has already made ox-biodegradable plastic compulsory for a range of plastic products including food sold in supermarkets.
The European Commission though has expressed concern about the length of time plastic might take to degrade, concluding the technology was not suitable for long-term use.
Laurier added Symphony has submitted evidence to the EU Commission that d2W plastic will fully biodegrade with a reasonable time, more much more quickly than ordinary plastic and into non-plastic bio-degradable material.
He said he hoped the BBC programme would start a debate about the solutions available to deal with the plastic waste problem, including d2W.
Shares in Symphony fell 24% to 15.75p.