Electric = CYMA usually Glock CM030 - fires at about 200fps but has full auto
GAS - either Green Gas (propane) or CO2
CO2 is a bit more powerful than GG - aprox 450-500fps Vs about 330fps for GG pistols
cheaper pistols are non-blowback from about £35 for cheapy non-blowback
& you can pay over £100~£150+ for top of range blowback pistol
not tired this one but has the option of buying a CO2 mag as well as standard Green Gas mag
https://jdairsoft.net/asg-cz-p-09-duty-inc-case
CO2's are a little too "hot" or powerful to use at most sites being that a fresh CO2 bulb can be firing at
say 550+ at first - coming down to about 400-ish after a dozen or so shots, should get say 2 or 3 mags
out of a CO2 cartridge before it needs changing - but depends on mag/gun
also blowback pistols will use a little bit more gas due to blowback action
GG pistols are a little less powerful and can be used for skirmishing at airsoft sites
CO2's will need a little modification to lower the power
as you may just be using for backyard plinking then very little of this really matters I guess
if you was gonna be using the pistol a lot - quite a bit at sites then GG pistol & propane adapter
maybe if you can find a HFC 104 or 105 GG or CO2 version if you are really lucky & low budget
CYMA CM030 will be about double that price aprox
& top blowback gas pistol would be even more
but as you may be using it for the odd target practice then either of the 3 types would do
there is the spring versions but most here use spring snipers or shotguns not pistols
one more thing that I failed to mention - Gas guns can suffer from cold & leak
as you in Scotland it might be worth looking at cyma cm030 as it will operate in cold
but CO2 is "slightly" less prone to failure than Green Gas I think but still can fail
(All gas stuff can fail with seals - it is a weakness they all have)
but electric pistols are way down on power but will be fine for your targeting range/distance