Wills Act 1837 - Wills are not valid unless:
The Will is in writing and signed by you (the testator).
You sign under your own free will and not under any duress i.e. by signing it is your intention that the Will comes into force.
Your signature is witnessed in the presence of two or more witnesses and they also sign to confirm their presence when you signed.
Coronavirus and self distancing:
In these extraordinary times, we have seen a story on the BBC of people attaching Wills to windscreens, signing and then backing off a distance whilst the witnesses sign. We are also aware of some clients where Wills have been signed whilst the witnesses are outside looking through a window. We would find this hard to disprove that the witnesses were not present and some old case law Casson v Dade 1781 (thank you techlink.co.uk) highlights that it may be sufficient for two witnesses to have ‘line of sight’ when the Will was signed although not in the same room.