On the 31st July new rules will come into place around the storage of "air weapons". In brief It will be an offence if they are not stored securely and out of sight of persons under the age of 18 and compatible ammunition also needs to be stored seperatly.
https://www.legislation.gov.uk/uksi/2023/768/contents/made
An "air weapon" is defined as having a power of over 1 Joule so this does not apply too Airsoft type guns. They have not defined what "securely" means, but it does not have to be the extent of a gun safe, many are assuming that a locked room or cupboard will suffice.
Airgun Law Change