Ainsworth, who owns and runs At Number 6 and Rojano’s in the Square in Padstow, was presented with the accolade by Anthony Pitcher OBE, chairman of the Board of City College Southampton.
“My time spent at City College is the reason I’m where I am now,” he said. “I still use the knowledge and skills I learnt here today and I can’t thank the college enough for what it’s done for me.
“I am very proud and overwhelmed to receive this honorary diploma and it will take pride of place in my restaurant.”
Ainsworth last year took part in the BBC2 TV series Great British Menu, and last month cooked a six-course fine-dining dinner with fellow chef Nathan Outlaw in a live online masterclass.