TS do not always get the rules quite right!
Pig feed can (but rarely does) contain fish which cannot be fed to ruminants.
If you pig feed does contain fish, then you should be able to demonstrate that you have adequate procedures in place to ensure that it is not fed to sheep etc. I don't directly know of any law that says they MUST be kept apart, as far as I am aware it is simply a legal requirement not to feed fish to sheep, and TS would need to prove you were doing so in contravention of the law, rather than that you are creating a risk or potential that this might happen. If someone knows differently (ie a law) then please let us know, i have found nothing so far.
However if you had pig feed containing fish and you showed them an environment where for instance you could not tell them which scoop you used for what, then they could put a case together to say that you must be feeding fish to sheep as you are muddling containers/scoops etc.
Clearly best advice to avoid this would be separate storage, and if there are employees signage etc. might be appropriate, but this would be sensible guidance rather than a legal requirement to my current knowledge.
HOWEVER If your pig feed does not contain fish (most don't and the label by law has to say do) then there is no reason why you should not keep the two together, and there is no legal reason to separate as there is no risk. It is obviously easier for TS to simply say keep apartin all cases.
Now sheep and pigs need different dietary requirements, and you should not generally feed food of one to the other, but this is a health issue rather than a legal requirement, and if your feed does not contain fish, I see no reason why TS should insist on any separation.