Is it too late to start again?

It's worth a try, surely 

Not too late at all I reckon. I sowed some a while back an early variety and they will go out this weekend. I sowed another batch just yesterday. Quite confident that  in a normalish year the second lot will do just fine.

Last year was my first for trying to grow anything. It was maybe the second week in June, and I had an urge to grow my own oriental veg's for my stir fry needs. The next week I was ordering seeds all over the place. I just got that itch for a new interest.

I'm in the Midlands, and last year I sowed some mini munch (F1?) sweetcorn maybe the beginning of the third week in June. We had some good sunny weather, but also a lot of rain and flooding. It was genuinely two ends of the scale, as I remember. I only wanted to grow sweetcorn for the aesthetic, at the time. They did really well, I think (nothing to compare to at that point). Picked cobs late August (?) maybe September. Awesome.

I'm still a noob, but I would suggest going for it, if you have the room. You never know what the weather is going to bring. Late summers seem to be more of a thing these days. I don't know about Scotland, but again, if the room is there; I would relish the fun. And even if they don't do so well, use stems to grow beans or peas up. At the very least, you will have some lovely stems and palm-like leaves to enjoy, if you are someone that enjoys that kind of visual appeal.

If not then, like I suggest, use them as bean/pea polls and you cannot lose in terms of possible space wasted.

Regards

I’m planting some squash in the same bed, so they’ll use the area even if the sweetcorn fail!

Okay, so you could do the three sisters thing (not too late, given some good weather), depending on your bed. That's what I'm doing. If the corn doesn't do well as a productive crop (if that's your goal), then you can use them as poles to grow beans up, and your squash does it's thing on the ground level. If not beans, consider peas. I'm not an expert, but sugar snap peas did their thing last year for me. Again, I started late in June. Use the space. If the sweetcorn doesn't work out, you'll still have two other things in the same space that possibly will. The peas almost certainty... even if you happen to be on the very Northern tip of Scotland.

Do it, rock it, learn from it. Enjoy any failures. Everything to gain. Unless there's another aspect you haven't mentioned to make me feel different. So far I don't see that.