I just came up with idea that coffee is so popular because people can't find suitable tea. I didn't make any research yet how popular is the loose tea in UK (because I brought some from my home country which doesn't produce herbal tea, lol) and Tesco Metro doesn't have much choices of loose tea. However, different loose tea tastes really different. I mean, different coffee also is not the same, but it can't beat the variety of tea. My favourite ones are Earl Grey and Chinese Gunpowder, but occasionally I buy random Indian black tea, white tea when it's hot outside (YES, tea and especially white tea helps you to reduce the temperature of your body) or Sencha.
Advantage of tea is that it's not addictive, but it also simulates your body (mainly black and green teas) and it doesn't affect your teeth colour so much. That's why people who enjoys both coffee and smoking have (less or more) yellow teeth. Moreover, tea also can be drunk at any time (maybe not so strong tea/green tea before sleep, though) and it can be as a part of meditation.
By the way, are tea rooms popular here? I have seen some of them, but I didn't try them yet. I've been invited to a tea room in Czech Republic and I enjoyed that atmosphere of pub without selling alcohol drinks. You simply buy some tea, you get a thermo bottle and two special mugs – one for preparing tea, other one for drinking tea (so you can control both the hotness and strength of tea by yourself). It should be the same in UK, I hope.