It was fit for use when it was introduced, has been for some time, and is adequate for many episodes of care but it is now past its sell by date.
It can be patched to make it usable, probably, but it may actually be better to separate its various functions.
Computers permit this without a perceptible increase in errors or effort or cost.
A handwritten addendum greatly increases cost, greatly increases the potential for error, is rarely designed well, accentuating those last faults, scales extremely poorly, and is very expensive.
Handwritten addenda are more common and likely to become more so.
Some of them could be substituted for by carrying a printer and producing sticky labels, as done in 1984 for such tasks as intravenous feeding regimes in some places with an Epson carry-able computer.
The problem, and the solution are likely to be unappreciated by those focused upon hospitals, which regrettably includes those in charge of district nursing and nursing home regulation. They lack the background. They may be educable.
Event-based financial system used, holding state needed.
The problem is that the FP10 form is overloaded. It is an accounting token, a workflow token for pharmacy, a set of instructions to a patient, and it is not, and never has been, a complete list of what the patient should currently be taking, and how.
It is also used as an indication of what GPs prescribe, a task for which it is of course the least good record.
A solution is to automagically produce a state document – IE each time a change of medicines occurs,
This is something which should come via doctor-driven development of IT systems, and introduction of it without IT support – automation – should be opposed vicigorously
 it has more than one function.
If you substitute for “prescribe” something about what pharmacists admit to having dispensed for patients then it is marginally more accurate, but it does reflect as well as could be done the prescribing intentions of GPs which oddly is what the people looking at these analyses claim to be or should be trying to understand and sometimes influence.)