Based on Davey's history, I do have some serious concerns here.
First as he is an older lad and we don't have the risk of a car accident or similar trauma, our 2 main concerns are paralysis due to spinal/nerve compression or secondary to a blood clot. I would note that his situation doesn't quite fit (with the lack of tail/rectal nerve function loss) with a clot but is a concern if he has no pulse in the leg and if it perhaps is colder then the other leg).
Now to have one leg paralyzed and the other normal, again clots lodged are a concern but this is also something we see with one sided spinal lesions (ie abscesses, blood clot in the spine, tumors, discs compressing the spine, etc). The space occupying item tends to compress the spine and nerve function is lost. We can see this also with peripheral nerve compression but to hear we also have tail and rectal nerve function loss makes the spine more likely to be affected (since it would take a bigger mass to compress the nerves for all of these at once, if you know what I mean. And that is why a blood clot in his blood vessels here is less likely too, since to affect all of these, we'd expect the other leg to be showing signs too). And I would note that if we have a large enough mass or it is one involving the lymph nodes (like lymphoma), then this is going to cause that swelling you are seeing in the foot. This is essentially due to poor venous drainage or reduced function of the lymph drainage system of the limb (since we all leak fluids into our tissues from circulation and the lymphatic system picks that all up so we don't get swollen). So, this will be a side effect of the main issue.
With all this in mind and the lack of any tests, I would advise treading with care. Since we have the risk of a spinal tumor and something that could be progressive, we don't want to rush to amputate this leg because we cannot say that this won't cause issue for the other leg in time. As well, we really need to know if he has bladder function and control (though I suspect he does if he isn't dribbling due to an overstretched non-responsive bladder already) since that is critical for life. Instead, we'd need to think about at least an xray (to see if there is a mass around the spine or outside of it) or ideally a CT or MRI (so we could see into the spinal canal itself). This would help us start narrowing down what is causing this loss of nerve function. Depending on which issue was present, it may be treatable, but I do have to warn that spinal tumors can require chemo or surgery and even then have guarded prognoses. Otherwise, if after testing a clot was still suspect, then he may benefit from a heart scan (since this is where the clots originate from) and may need to be put on blood thinners to prevent any more occurring.
Overall, I am concerned about Davey. His signs are just very suggestive of a spinal based issue compressing one side of the spine. And I would not want to rush to remove his leg since at the moment there is a risk (due to not having a definitive diagnosis yet) that we could loose nerve function in the other leg if this is a progressive issue (like a tumor) compressing his spine. So, we need to tread with care and I would say that if you are not confident in your local vets, you may want to consider requesting a referral to a vet neurologist or checking the ACVIM website for one near you HERE.
Please take care,