Bus drivers managed to enforce the smoking ban when that came in. If an eating ban had the force of law it should be a similar situation (and IIRC▸ smoking was banned on buses before the general public places legal ban).
The big difference is that everybody eats, far from everybody smokes, and no-one ever got sick through passive eating. Members of the public were prepared to challenge anyone lighting up, and it quickly ceased to be an issue. In my local village pub, by the way, there was a discussion days before the ban came into force, with a small number arguing that the police hadn't been seen in the village since one got lost in 1978, so we can just carry on. Then one asked the landlord, patiently listening, what his view was. In a nutshell, he would ban anyone who tried it. It's the law, his licence would be in jeopardy, which is the other side of Devon, and he hasn't liked cigarette smoke since he managed to kick the habit.
But food - I usually set off on a long train journey with a decent packed lunch and a couple of tinnies or a small bottle of something, but not on the bus. Maybe a polo or similar, but how many would I need to eat to fall foul of the law, I wonder?
This is the same Dame Sally, btw, who told us there was no safe dose of alcohol, prompting many to quit counting, and whose fatwah on red meat has recently been overturned by somebody who is paid more. She is missing the point anyway - scrap public transport on the assumption that everyone will walk, and we'll all be fit as butchers' dogs in no time.
Happy retirement, your Ladyship, good luck in the pantomime season, and don't tread on any mines. And greet broadgage for me if you see him...