Thanks! I've got access to a few accessibility charities where I can borrow short term on a set track which is fine but I'm looking for something I can keep so I don't feel as precious about looking after it and leaving it unattended anywhere.

The the link was pretty useful because it seems what I'm looking for is called a wheelchair cycle - https://www.pedall.org.uk/bikes/wheelchair-cycles/ that should give me a pretty decent workout!