I do want to be able to do button holes, so that would be a deal-breaker. What do you think of the JL machine that's £99? - it looks like a step-up from the £59 model.
Ah, this one must be new, I've not seen it before. It has buttonholes, but still not speed-control on the foot pedal (and I can't seem to find if it has a light or not). It seems like you're not getting that much in the way of features for double the price and weight, in my opinion.
I think if you're going for a more fully featured machine, you'd be better off going for something like the Janome SnowLass linked to. I *think* that's the one my neighbour picked up a few weeks ago which I played on when he came calling asking if I'd show him the basics. If so, it was a good machine! But it's £199, which is a step up in price again.
I'm a bit surprised that buttonholes are such a killer feature for you, though - in the realm of fastenings, you've got snaps, hooks and eyes, zippers, ties, and even velcro that can be done on the little machine, and even bound buttonholes or *gasp* handsewn buttonholes if you're that way inclined. Maybe it's because I hardly ever wear button-down shirts, but I really only ever end up using my machine's buttonhole feature when I make trousers, and in those cases I could just as easily use a trouser hook or hammer-in snap instead.
I dunno, it just seems to me that if you're going to spend £100 on a machine, you might as well go the whole hog and get one with ALL the features rather than an in-between model you're less likely to upgrade from later. Or go for the cheaper model and treat it like a starter machine and know that you can upgrade later if you end up doing a lot of sewing.
Edit: Or another option for you might be to buy a vintage machine, as the pre-1980s models were all metal body construction and were built like tanks for everyday sewing. They're heavy beasts, by and large, but will do all the things you want for a lot less than £100. Even repairs on vintage models are usually under £20 if you know anyone in the family with one they're not using...