There is no law dictating how a Will should be stored. It is entirely up to you what you want to do about storing your Will, but there are some common sense considerations.
It must be kept somewhere secure, where it will not be misplaced, damaged inadvertently, or thrown away. You should tell your executors where it is because they will need to find it if you die.
Bank deposit boxes are not a good idea for storing a Will because the bank cannot open the deposit box until probate is granted, and your executors will need the Will to obtain that probate.
Wills can be stored for a fee by HM Courts and Tribunal Service. You can learn more about this service by visiting their website.
Wills are kept by some solicitors. They will sometimes do it for free, and sometimes they will charge. Here at MWQ, we have recently begun encouraging our clients to store their own Wills and notify their executors of their location, as we believe this allows the executors to easily access them when the time comes.
Wherever you keep your Will, it is critical not to staple it, use a paperclip, or put anything else on it that may mark it, as this may raise the suspicion that there are other parts of the Will that were attached but have since become lost, causing problems for your executors and beneficiaries.