11pm and cornflakes
The article says everyone should be out by 10. I'm fairly sure the new rule is 11, although they have to make their last orders by 10.
The regulations themselves don't actually contain the phrase "substantial meal" and I reckon you can get away with serving cornflakes.
The Health Protection (Coronavirus, Restrictions) (All Tiers) (England) Regulations 2020 say that the meal must be "such as might be expected to be served as breakfast, the main midday or main evening meal, or as a main course at such a meal."
They're here:
https://www.legislation.gov.uk/uksi/2020/1374/made