Another 50 Sainsbury’s Locals are coming to London and the South East by early 2014, bringing the total number in the region to 200, the retailer has announced.

The move is further confirmation, in case you needed it, that convenience is BIG. Sainsbury’s has opened 87 c-stores in 2012-13 alone, and has 523 nationwide. IGD analysis confirms that convenience is a safe bet: it predicts the market will grow 29% over the next five years. Sainsbury’s itself has enjoyed 18% growth in convenience in just the last year.

C-stores, the multiples argue, breathe life into moribund high streets and create jobs: Sainsbury’s says growth in its c-stores will create 10,000 jobs over the next three years. Though there is also a trend for replacing staff-run tills with self-service points, as was the case at my Local in Streatham Hill. This was a great pity, not least because the staff there are so insanely cheerful (I wondered, more than once, what Sainsbury’s was pumping into the air…).

But there’s a flipside to all this rampant growth: strolling up Streatham High Road and Brixton Hill is like passing a cartoon backdrop on repeat: there are four Sainsbury’s Locals in the space of two miles, plus a Tesco Express and a Co-op. But the nearest superstores are miles away.

It’s not just my imagination - it’s strategy. At its trading update last week, Sainsbury’s CEO Justin King said: “Probably about half of our new c-stores were within the M25. Because of the high population in London there is a lot of scope for stores and you’ll see them more frequently there - sometimes quarter of a mile to half a mile apart. So there is a fantastic opportunity to add more within the M25.”

“I already have five Sainsbury’s Locals within 1km of home, +1 superstore. Really don’t need more,” said one of The Grocer’s followers on Twitter. I sympathise. Expanding your c-stores is all very well, but sometimes you just need somewhere to do your big shop. It’s not that convenient when you realise your c-store doesn’t stock that ingredient you need, or it charges more than a superstore might. Don’t city dwellers deserve access to big supermarkets too?

As for rejuvenating the high street, Sainsbury’s Simon Twigger says the new c-stores “will give a real boost for other retailers as they bring increased footfall and trade”. But others cry that the big retailers are squeezing out independent traders. How, then, do you solve a problem like the high street? Well, the government is trying a new tack this week, putting aside £1m and calling on the Association of Town and City Management (ATCM) to improve the leadership of groups set up in the wake of the Portas Review.

I hope the ATCM plan makes a difference. And I hope that some of that Portas cash finally gets spent. Otherwise I fear that cartoon backdrop will keep repeating in our towns and cities, until the big retailers have a c-store on every corner. Convenient? Yes, but only up to a point.