I found two programs, each does the job. I thought UNetBootIn was better than the Universal USB Installer, but this was because UNetBootIn works under 64-bit Windows. Apart from that, either would be fine.
It looks basic, but it works.
It gives you the option to download the ISO directly from the internet. Useful, but I’d prefer to download a copy myself, so I can re-use it later.
If I had a complaint, it is this: