Unfortunately, you will need an adult with you if you plan to order alcohol with your meal.
In the UK you can consume alcohol at the age of 16 alongside a meal, but only when accompanied by an adult.
I've worked in several restaurants and bars, and although the premises' alcohol license may also have stipulations (for example most nightclubs are not allowed to serve under-18s under any circumstance), restaurants and pubs which serve food can serve beer or wine to 16 or 17 year olds, so long as they are also having food, and are in the company of a responsible adult.
You can get more info on that here: https://www.gov.uk/alcohol-young-people-law
The same law covers the employment of 16 and 17 year olds in places serving alcohol too. So long as the alcohol is part of a meal, it'd legal for a 16 year old waiter to serve it.
But it would be illegal to put a 16 year old behind the bar of a pub or club, where patrons are there with the sole purpose of consuming alcohol.