I have recently been researching the rules and regulations regarding shooting in my backyard. While there are specific rules for air rifles with a muzzle energy of less than 12ft lbs (the legal limit in the UK), such as not shooting beyond your property boundary, using an effective backstop, avoiding discharging near public roads or footpaths, and not causing distress to neighbors, I have been unable to find any information regarding the use of air pistols or airsoft guns.
All airsoft guns are much less powerful, and even if a BB were to ricochet, it is highly unlikely to cause injury. Most airsoft guns have an energy level of around 1-1.5 joules, whereas airguns can range from 7 joules for a pistol to up to 16 joules for a sub 12ft lb rifle. Additionally, airsoft guns fire plastic BBs weighing around 0.2 to 0.25 grams, unlike steel BBs or pellets used in air rifles. Even a .177 caliber pellet weighs about 8.5 grams, while a .22 caliber pellet can weigh up to 16 grams or more. This is why many indoor airgun ranges, where people use air pistols to shoot knockdown steel targets at a range of 6-10 meters, are now prohibiting the use of metal ammo due to the risk of ricochets. Though the issue is not as severe at 25 meters with rifles, there are still a few instances.
Furthermore, these airgun ranges are not only prohibiting the use of metal ammo but also providing airsoft pistols to pistol shooters for safety. However, this raises the question of whether air pistols will ever be considered a valid form of defense, as individuals will be unable to use them, except for precision target shooting, which represents only a very small minority of air pistol shooters. It is worth noting that precision target shooting at 6 meters is not typically done with gas blowback or CO2 pistols. I apologize for the rant, gentlemen.