Okay, first thing, you do not want any gun that costs under £80, it will break and will not be capable of hitting anyone at a decent range.
Secondly, as you are under 16, most sites will require an adult to play with you. This means you pretty much have to persuade a parent or other family member to take up airsoft. You may as well therefore wait for that adult to get UKARA registered (2 months from the 1st game with 3 games played at the same site) and then get them to buy you a non 2 toned gun.
Ignore the sidearm, no-one needs a sidearm and put all the money into a decent main weapon. If you really want a ww2 weapon, then when a parent has sorted out UKARA it will be possible to import one from Poland without any issues.
http://www.taiwangun.com/en/agm-058?from=listing&campaign-id=19
Otherwise look at something like a G&G combat machine.
The difference between the 2 is vast. The G&G combat machines are very good beginners guns, they are well made and shoot well. They are made of good quality plastic that can take a lot of punishment and the internals are good quality. They are modern guns so you can add sights and other accessories easily. The ASG sten (AGM if bought outside the UK) is not really a beginners gun, it has no fire selector or safety, so you have to not pull the trigger by accident. It is made of steel so if you drop it, it will break your toes not the gun and it shoots really well (they are so good the German players complain about them being too good). You are stuck with just ironsights and because they are full auto only you cannot use them indoors (there is a way around this by using a burstwizard mosfet, which is a tiny circuit board you plug in between the battery and the gun).