I’m British. Reading this thread is like the last 20 years never happened. Nigella and Jamie will be so disappointed.
I wouldn’t sweat it, mate. The whole idea that an entire “national cuisine” can be bad, or unpalatable, must less “the worst” is a ridiculous notion. Anyone who can offer a serious answer to the OP’s questions isn’t operating at a level that should bother you.
Yeah, I mean, just look at some of the cuisines suggested in this thread. Probably all my favorite cuisines in the world have been mentioned at one point or another. I lived in Britain in the mid-90s, and found the food there to be quite wonderful.
Except for Nepal.
Spoken like a man who has been to Mali.
My own least favourite that I’ve tried a lot of is also Phillipino.
But then I haven’t tried most African cuisines, despite having access to their restaurants (in the UK, so maybe not truly authentic and obviously not the same as home-cooked food anyway). I’m vegetarian and those restaurants usually don’t offer a full meal for me even if I order multiple side-dishes, which I’m happy to do instead of ordering a main course; the sides are just starches all the same colour and flavour, so I go elsewhere.
I think any national cuisine that can’t do something tasty without using meat is doing cooking wrong. I mean even for meat-eaters, because it implies that the cooks are unimaginative and have a very small repertoire, relying on just giving you MEAT rather than cooking well. Some countries famed for their meat dishes also do some awesome veggie or bean-based dishes, either as sides or mains - France, Italy, Vietnam (someone above mentioned Vietnamese food as being awful, but they manage to make tofu taste amazing), Japan, Korea.
I actually find it quite refreshing that British food has been mentioned so little. People have learned. 
From my vast experience*, a lot of the improvements aren’t even a matter of doing anything particularly exotic, so much as treating better what is there. Even something as simple as a breaded slice of fish is a lot better when it’s cooked right before serving than when it’s been fried whenever and kept in a pond of warmish frying oil.
- Not particularly vast, but it does cover 30 years and multiple locations and price ranges.
No. I didn’t mean that British people have learned, but that others have.
And fish and chips does not involve breaded fish. The fish in that dish is battered, not breaded.