I honestly don't think that the "gun cupboard" was a properly designed gun cupboard? My stepfather had a steel lockable gun cupboard built into the lintel of one of the doors. The opening of it was also contained within a lockable room. The police had to examine the cupboard every year to make sure it adhered to regulations. A cupboard under the stairs would not have been legal.
BS7558 didn't come into force until 1992. I'm not sure what there was before but that's what current legislation refers to in the 2005 Firearms Security Handbook.
But by Jeremys own words (or at least those on his official site):
http://www.jeremy-bamber.co.uk/myths-facts
Nevill Bamber left guns around all over the house they were hardly ever locked away in the gun cupboard which was not a metal cabinet but a built in cupboard. There was a gun in almost every room this was how farmers lived 25 years ago before the gun laws were tightened.
I was shot down in flames for pointing this out a few months ago. I was then told that it wasn't Nevill who left these guns all over the place, but Jeremy, in an attempt to cover his tracks.
I do, however, have the experience of visiting my family who have lived in D'Arcy and nearby villages since the year dot - and of course my family's advice on this. When I visited my Great Aunt Kate and my mother's cousin, Ginger, I sat down on a chair only to find myself sitting on a rifle.
"Move your pop gun, Gt Auntie told Ginger, you're froightenin' Kerra"
"Not really, Auntie", says I, "I had a go of it when you were out yesterday!"
"Shuddup, Kerra!", says Ginger.
"That's noice, dears", says Auntie.