Keeping only a single copy seems insane to me, any number of things could go wrong and destroy all that's stored there[1]. Digital copies wouldn't so bad if there were redundant backups (tape[2], film[3], etc.).
[1]: https://www.cbsnews.com/newyork/news/nypd-warehouse-fire-evi...
I don't know about the UK, but according to an old episode of Dallas that I watched recently, in the US there are usually three official copies of a will kept: one in a government records office, one at the office of the lawyer who drafted it, and one with the individual.
It sounds like this proposal is for wills >25 years old, so the biggest impact would be on historical-research use cases.
Pretty much all that needs to happen in the US is somebody shows up with a document signed by a few people (dead guy and some notaries). Whether that document was stored under the fridge or a law office -- nobody cares.
Not a lawyer, but uh talk to people before you make a will to see if there's certain possessions that they want. Maybe you have a signed baseball that your brother was in attendance at and he'd want it when you die. It'd certainly look weird if a bunch of people you knew showed up at probate court saying you said you'd give them X item and the (forged) will only showed everything going to the housekeeper.
There's a bunch of old celebrities coming up; you could try forging their wills and see how it goes ;)
[1]: https://www.google.com/search?q=tiger%20king%20forged%20will...
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