Don't give a f*** to be honest.
Sometimes it is good to have been classified as "Disabled and unfit for employment"
But to answer your questions ~ Doctors have already said that they do not and never will know enough about their individual patients' various employments and the tasks that they may involve. The doctors guidance from the BMA is clear. The GP must state whether he/she considers the patient to be fit to work or not (as opposed to being too ill to work as has been the case). The GP is now able to qualify that "Fitness to work" statement by saying that the patient may not/should not, in the course of their duties, be expected, in the case of back pain or pregnancy for example, to lift, carry etc The GP may write that the patient should not be subject to stress or that they may be infectious for up to a given period .... and so on, dependent upon the diagnosis.
In my case the GP would be able to state that my heart condition makes it impossible for me to climb stairs, stand for protracted periods, walk more than 50 yards and that I am subject to sudden heart stoppage that will cause me to effectively die but that the implanted defibrillator will probably shock my heart into re-starting. It would then be a matter for the employer to seek advice from their own retained doctor or from their insurers as to (i) the type of work that they could reasonably expect me to be able to do and (ii) whether the insurers will be prepared to provide cover for me. In my case it is unlikely that the insurers would agree to provide cover under the employer's "Employee Liability Insurance" and thus the employer would not agree to my returning to work.
Same will apply to most illnesses. If the GP says you have Typhoid it is unlikely that the employer will want you infecting the rest of the workforce.
Why worry about it? Surely you can see that this is simply another idea that Government have come up with trying to look as though they are doing something about the work-shy and that it will not really change anything?
