Barber - who was awarded the OBE for services to the environment in the New Year Honours List - travelled to Windsor Castle to receive the accolade.
The Queen told Barber his work "sounded like a good cause" during their meeting on 7 April.
"I was a little bit nervous but I am now keeping the presentation box open on the bookshelf to remind myself of the day," Barber told HW.
The former head of parks at Bristol City Council and CABE commissioner said he was delighted to receive the OBE and share the experience with his wife Jan and daughters Vanessa and Fiona.
He added that he took his medal to Bristol's Southmead Hospital - where he is receiving dialysis treatment - to show to nurses who have been caring for him.