Waitrose's self-service tills don't make you weigh things. But they seem very prone to double-scanning. I think you have to do more waiting for staff to come and rectify things, unless you're very careful; you want to pack directly into a bag, rather than putting things down and picking them up again. (Especially after you've paid, when it is quick to assume you're someone else and start scanning again.)

I'm all for increased union membership, if only as a political statement. And you're in a large enough organisation that if the union rang them up and told them of a snafu they'd probably listen; I do hear tales of repeated snafus in universities, though not specifically Dundee.

I'm in Unite, but if I had an actual problem I'd go to ACAS first; ACAS are brilliant, and free, and amazingly under-advertised, which is presumably how they can afford to carry on being brilliant.