If you are used to target shooting, airsoft probably isn't for you. If you are happy with how your spring airsoft gun is working and shooting then this post doesn't really apply - and I'll add a bit right at the bottom for decent two tone AEG's.
You should understand the mechanics of pellet flight - and how hold over/under works depending on range. Well airsoft is that on steroids, The flight of our BB's is loopy and we aim to hit man sized targets at range (40m). If you think that you will get groupings that are controllable then think again. Typically a pistol at 20 meters should be hitting a 12" target - note that is hitting and a few inches of spread at that range would be considered normal.
I'm quite lucky that my local range allows airsoft and air rifles, and I can tell you without exception every air rifle shooter that has shot my airsoft gear has laughed at how inaccurate they are. They all get in on the sights and aim for the small spinners at 20m and without fail they miss by a mile. The guns look good, but they have no accuracy. It's made all the more amusing as my air rifle is actually pretty well setup - been a Bowkett blueprinted bsa S10.
Airsoft has other advantages. The BB's are shot at around 1 joule (12ft,lb is about 16 Joules and 6 ft,lb 8 Joules). So it is a weak low powered shot that for the most part isn't going to do any damage. It can still pepper soft walls, and we wear eye protection as we shoot at each other with them. The guns are quiet, but a pcp with a shroud is 100% quieter.
Airsoft ammo is cheap 3000 rounds is about £8. Compared to 500 .177 pellets at £10, or 500 .22 pellets at £14. Regular (non bio) bb's don't typically degrade in storage, and out guns are allowed to have semi auto and full auto modes, fed from magazines. Typically with either gas in the mag as a Co2 bulb or propane lighter gas, Or driven by a motor and battery in the case of automatic electric pistols (AEP) or automatic electric guns (AEG).
Our guns are allowed to look realistic - but the cost of that is unless you have defence for purchasing an airsoft gun (Ukara) then you are limited to high visibility coloured guns called two tones. To get Ukara you have to be a member of an airsoft skirmish site, and play 3 games over at least 2 months, After that they issue a number so you can buy without two tone. Unfortunately there is no way around this, FAC, Shotgun licences do not migrate. Once you have the guns there is no other ownership requirement other than not alarming the public with them as they look real and the police will treat them as real if they get called out - until they can be proven safe.
Personally if i wanted to 10m backyard plink I would consider a bell target rifle. It's a sport that is often done indoors in pub backrooms. The guns are accurate, and the bell targets are fun to shoot at. You might also find a local league that runs. You should be able to find 6ft/lb springers but it might take a few calls to RFD's to track them down or have a 12ft/lb one downgraded.
http://www.belltarget.com/
Right - if you are happy with that springer airsoft gun then you might want to have a look at something like a Cyma AK or a G&G M4. The G&G doesn't come with a battery or charger - you need to look out for that with airsoft. Typically a battery is less than £10 and a cheap charger is going to be £15 but those cheap chargers are typically frowned upon and most people advise a smart charger like the skyrc B6AC that retails for about £40 - just be aware there are a lot of fakes out there, I think hobbyking sell genuine ones just make sure you get the correct plug type (uk). Also beware that Airsoft batteries on the hobbyking site are in lifestyle>airsoft. We have a different polarity to remote control cars.
https://bbguns4less.co.uk/products/cyma-cm522u-ak47-with-folding-stock-in-blue.html
https://www.patrolbase.co.uk/g-and-g-armament-combat-machine-cm16-carbine?pv=5072