Again, generalizations are dangerous. Below is described what everybody knows about – but this is not necessarily what everybody does!
Breakfast is usually a packeted ‘cereal’ (e.g. cornflakes) and/or toast and marmalade. It isn’t usually a ‘traditional’ British breakfast.
‘Elevenses’ is, conventionally, a cup of tea or coffee and some biscuits at around eleven o’clock. In fact, people drink tea or coffee whenever they feel like it. This is usually quite often.
Lunch is typically at one o’clock (any shops which close for lunch close from one to two). But it is often a bit earlier for schoolchildren and those who start work at eight o’clock.
For the urban working class (and a wider section of the population in Scotland and Ireland) tea is the evening meal, eaten as soon as people get home from work (at around six o’clock). For other classes, it means a cup of tea and a snack at around four o’clock.
‘Supper’ is the usual word used for the evening meal among most people who do not call it tea.
‘Dinner” is also sometimes used for the evening meal. It suggests something rather grander and eaten comparatively late (at around eight o’clock). It is associated with relative formality (many people talk about ‘Christmas dinner’, even if they have it in the middle of the day). It is also sometimes used to refer to the midday meal in schools.