I think Tesco should put their own house in order first.
My local branch shows blatant poor management, many signs that the customer is a bit of an inconvenience, some poor staff attitudes, goods of deteriorating quality, terrible services and facilities.  And plenty of sheer incompetence.
They should forget the World Cup and remember their daily customers.

My local Tesco Extra seems to rely on customers using those self-service tills, which are always breaking down. I refuse to use them though, and stand there obstinately until a member of staff stops loitering in the aisles and chatting and serves me.

Don't care - I'm doing Tesco a favour by shopping there. Do they think I  should do their job for them as well?

Next few times maybe you should, when they finally turn up. plonk your basket down, or park your trolly at the checkout and say something like "It's ok, you obviously don't want my custom, so I'll go somewhere that does." And walk out.
I know that would be a bit inconvenient for you, but a few times of that happening, and hopefully they'll get the message.

I have to say, our local Tesco is great - all the staff are really friendly and can't to enough for you

Ours is pretty good too. It's a huge 24 hour Tesco Extra on two floors.

In all fairness the staff at the tesco I shop in are really friendly and helpful.