Anne Philpot was honoured after 25 years of service in the same year that the company turned 40.
"They are a good bunch here and we are well looked after," said Philpot. "Lots of people have been here a long time, which says something about how we are treated."
Philpot joined the company as a seasonal horticultural assistant in 1984. She moved into the office the following year and has worked on the accounts ever since.
The firm was named the UK's most enterprising family business in the Barclays Family Affair Awards last year.