Mills is currently the vice president of the European Commission advisory committee for ornamentals and NFU representative for the International Association of Horticultural Producers.
He said: "I am delighted to be re-elected as vice-chairman to this working party which aims to keep the ornamental sector thriving.
"A lot of our problems come from outside of Europe so it is vital that we work to ensure unity within the working party."
He continued: "Other issues we will be looking at include a close watch on the review of the plant health directive as well as an examination of proposed legislation on alien invasive species.
"Then there are the ongoing questions of maintaining reduced VAT rates in certain member states as well as the need to lobby intensively for harmonisation at the lower VAT rate in all member states in order to increase consumption of ornamental products."
NFU horticulture and potatoes board chairwoman Sarah Pettitt said: "I am delighted that Lionel has been re-elected as vice-chairman of the COPA flowers and plants working group."His experience and knowledge of the European institutions gained over many years will ensure that the interests of UK flowers and plants growers are well represented."