I've not read the thread, but in my experience these short hours contracts are even more exploitative than zero hours contracts.
I have worked under a 4.75 hour a week contract, but under constant pressure to do extra hours to cover colleagues sickness, holidays, maternity leave extra. Most weeks I was working much closer to 30 hours.
I was really shocked to find out that holiday pay was only accrued on my contracted 4.75 hours, not any of the additional hours. Colleagues who were "lucky" enough to be on zero hours were legally entitled to accrue holiday pay for every hour they worked.
This equates to about a 12% difference in pay, and is bizarrely entirely legal within the letter of the law (but does seem to be against the spirit)
This wasn't a retailer, but a public sector organisation, who really should know better.
Thankfully, I now been promoted and now have better hours & holiday entitlement. But employers exploiting such loop holes (and their staff) seems entirely wrong.