Iuno, we don't have Mexicans in Britain? By Mexicans I mean the people, we have Mexican restaurants, though...
I was going to comment on how we don't have <insert ethnicity here> in the US, yet I've eaten <insert ethnic food here>, but couldn't actually think of an ethnicity that would work. I mean, I've never eaten Haggis or Balut, but we clearly have the represented ethnicities here. I'm sure there's some odd food somewhere that folks in the US don't eat.
That being said I've had Enchiladas and Fajitas before. Maybe Tacos didn't make the transition to this side of the pond. That or I'm looking in the wrong places?
To be fair, tacos are more of a make at home kind of thing than something you'd order in a restaurant. Mostly because they are so simple and basic that most people don't order them. A typical taco night involves the following:
Buy small corn tortillas. Put oil (seasoned+garlic+whatever if you feel like it) in a wide shallow pan. Set a plate/tray with paper towel on it to the side. One at a time, put tortillas into the oil. Cook until they start to firm, then fold over (but not completely flat), remove from oil and place on the tray. Repeat until you have the desired number of shells (takes about 1-2 minutes maybe to cook each one depending on how hot the oil is).
For fillings, brown some ground beef (you can season this or not, as you wish), cook a can of refried beans, chop some tomatoes, lettuce, onions, cheese. Have some guacamole and/or sour cream and salsa. Add a small amount of each of the ingredients to the shell until full (or overfull, which is half the fun). Eat. Enjoy!
The great thing about tacos is that since they have so many different things in them, you don't need to think in terms of entrees, sides, etc. Each is a pretty balanced meal by themselves. And they're yummy!