In some areas, you self-refer – that's certainly true in our part of the midlands. You ring a central contact number that's published online, talk to someone about what type of assessment you need, and they arrange the appointment. You may be able to find this out from information published locally online.
It might be a bit more complicated than usual to get an appointment at the moment. It's difficult to do a meaningful assessment unless the OT can visit to understand your home environment, find out what activities are most difficult, and see to what extent you're able to move around.
One tip I'd offer is don't be too hesitant about accepting offers of things you don't feel you really need just now. I once rang them to get my wooden wheelchair ramp replaced and ended up with a stair lift and a wet room as well, neither of which I thought were fully justified at the time. The difference they made was extraordinary, though, and even though I tried not to use the stair lift if possible to preserve function in my legs, it was a godsend on the days when I really did need it. The OTs were also planning ahead; I was in my late 50s, so my mobility is more likely to decline over time than it is to improve, and the team was acutely aware there's no guarantee that funding which is available now will be there in the future.
ETA: cross-posted! The OTs in the local adaptations team are only like to do that kind of work, rather than rehab – with ageing and increasingly frail populations, they have plenty of people to look after without needing to work across different types of service.
It might be worth trying to get some local info on how well your service works,
@JemPD. Ours is fab, and so is the one in the area where my relatives live, but I've occasionally heard reports of councils who seem to make it their business to fend off as many referrals as possible (which is bizarre because major adaptations are funded by central government, and this includes paying the council a fee for project managing them – but so much depends on organisational culture).