Ethel correctly points out that a will does not have to be a complex document. However, a will is totally invalid if it's not properly signed and witnessed.
Section 9 of the Wills Act 1837 (as amended by the Administration of Justice Act 1982) states:
"No will shall be valid unless�
(a) it is in writing, and signed by the testator, or by some other person in his presence and by his direction; and
(b) it appears that the testator intended by his signature to give effect to the will; and
(c) the signature is made or acknowledged by the testator in the presence of two or more witnesses present at the same time; and
(d) each witness either�
(i)
attests and signs the will; or
(ii)
acknowledges his signature, in the presence of the testator (but not necessarily in the presence of any other witness),
but no form of attestation shall be necessary."
So the simple answer to your question ("How would it stand up in law?") is that it would have no standing whatsoever.
Chris