What are the most popular types of tea consumed in Britain?
Your question suggest you don't understand tea in England! There is only one type of tea*. The questions that go with tea is the "milk and sugar" and how strong, not what type! If you go to a cafe and get a mug or pot of tea, unlike buying beer, you are unlikely to get to choose the brand of tea, it is just black tea.
*More recently along the increase in popularity of coffee, herbal and green teas are becoming more popular in the UK. But in general if you see tea on a menu, it means generic black tea.
It always amuses me when foreigners learn I'm a Brit and offer me exoticflavours like "Strawberry and Passion Fruit" or some such nonsense, assuming we're tea experts because we drink a lot of it. We aren't, but we know what we like.
Most Brits just drink black tea, but it must be strong and hot and with cold milk and in a cup or a mug. People outside the UK make tea that to us is way too weak, in a glass (honestly!) and made with water that's not boiling. All these are capital offences in the UK, as is adding hot milk or no milk at all.
PG Tips is the market leader, and the one I personally buy and drink at home.
Twinings and Tetley are in a battle for second place. Twinings is a posh brand that is making a lot of headway with their herbal range. Tetley is a "builder's" brand - in the UK, builders tea is brewed very strong, usually with milk and two sugars. Tetleys and Yorkshire Tea are brands you'd expect to see on a construction site, in a maintenance engineers' tuck room, or anywhere where people are doing hard physical work. There are the supermarket own brands, obviously, and some of them are quite good.