signing a will is covered by s9 wills act 1837
Signing and attestation of wills
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.]
here:
http://www.inbrief.co.uk/estate-law/formalities-making-a-will-s9-wills-act.htm
it says:
After attesting to and witnessing the signing of the will, the witnesses must attest the will by signing and acknowledging his signature in the presence of the testator.
which I as a retired civil service pen pusher ( NOT a wills lawyer - but hey Barmaid is and she may be along in a mo ) would re execute the will.
I had a bit of a poxy colleague and when he said: "I want everyone to know I have never witnessed or attested any document - far too dangerous", I threw my will he had attested ( but clearly forgotten ) into a fire and re executed it. The last thing I wanted him saying pointing at my will was: " yes that is my signature but I have NO idea what it is doing on a will "