Well I will answer that BM.
Where do I start - and these are a mixture orf my experiences, my many friends experiences, and my retail business experiences:
Bad attitude of staff,; unfriendly; unhelpful; can't crack a smile let alone talk to the customer; everything taken for granted that you will shop at Tesco (which I certainly don't now) with numerous other examples on line; refusal to sell alcohol to an adult because they have a "minor" with them who they think you are buying it for; ditto with cigarettes (many examples amongst us that have also made the press from time to time;" leaders" in selling sub-standard products that contain horsemeat; an "unfortunate" practice of spreading rumours that they are going to build a supermarket (in multiple areas) that immediately destroys the value and retail power of the businesses around the site and devalues the value of the land that Tesco then build on taking advantage of their destructive power; oh, and yes two weeks ago I unfortunately went with a friend who insisted on going to Tesco - went to the Ladies and never had I seen a facility throughout my retail experience like it - no toilet rolls, no soap, floors dirty, bits of toilet roll all over the toilet cubilcals and female hygiene bins overflowing - all an absolute disgrace for a food store as major as Tesco!
I am a dedicated Sainsbury's shopper have been since shopping with my mum as a child aged 3 years, who also uses Waitrose, Asda, and the likes of Iceland. What a different experience that always is, with staff in especially Sainsbury's always talking to you, smiling (one kept on not doing so and after my intervention they went!) and giving great service in great stores with lovely toilets!
Blimey Lizzie, you really are not a big fan are you ?

I have to say most of what you say puzzles me. My time is split between North London and West Wales and at the Tescos in both I don't see much, if any, of what you say. In Wales in particular, the staff are outstandingly helpful and pleasant, and chatty. Clean, nice toilets etc, with green hills and cows visible from the car park !
However I certainly have issues with Tesco. In particular the way in which they acquire sites, they bully and manipulate "We are Tesco and we get what we want" ! . . . . one way or the other. I know of one example where a large old shop in London agreed to sell to Tesco. Well into the process Tesco unilaterally reduced the price by £50k on a take it or leave basis. The owner pulled out and sold to Sainsburys.
Treatment of suppliers ? Numerous stories out there, despite the recent TV programme about their buying processes that was ever ever so . . . . "nice". PR crap
"every little helps" ? Yes of course many things are very cheap, and there are good deals. But across the board, they are expensive. Waitrose is frequently the same or even cheaper. No, "every little" of what ? . . . . how about Bull S ?
In London I shop mostly in a Lidl that is walking distance. In Wales, I try to use local town centre shops and the market, but also Lidl, but I do use Tesco and Morissons sometimes. In fact Tesco and Morrisons are almost the only petrol stations left. There is talk of a Tesco Express in the town . . . . . goodbye market ?