A copy of a will is just that a copy. It is not valid as an original will and usually no official body (i.e. courts for probate/letters of administration) would accept a copy as being valid. Most people keep the original will in a strong box at the bank or leave it with their solicitor who will have a document room which is usually fire proof. They only have a copy themselves usually so they can remember what they put in the will and so that the family actually know that a will exists when they are searching through the deceasedīs papers etc. Having an original will at home is dangerous in that it could be destroyed, thrown out accidentally or worse (as has happened in some cases) when someone who does not inherit as they thought they should destroys the will (since they may be better off under the intestacy rules).
A copy of a will would probably only be accepted by the courts etc if there was a genuine cast iron reason why the original could not be produced i.e. solicitors office destroyed in bomb blast etc...then they might accept a copy.