I asked my local site to buy it from wolfarmouries.co.uk. You can still purchase the P90 there, if you looking for one or a other Tokyo Marui, be quick since Tokyo Marui can't be imported anymore due to trademark trolling by Cybergun.
Shoot people with it.
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Yes, it hurts but doesn't hurt as much as doing Kendo unless you get hit on the thumb/nail which stings like a bee. Facemasks, goggles or glasses are a must, anything else you wear is down to you.
The guns can easy smash a screen on a mobile phone or a TV, pretty sure it could easy kill a bird or rat or something as well, it will also break your teeth if you get shot there with some high powered guns. But like I said, you wear masks so it's okay.
Paperwork, well all you need to own a RIF is to play three games at a local site and become a member there then you can post your UKARA form which allows retailers to check if you play or not to sell to you and at the same time it provides you a valid defence for owning one. Nothing is needed for a gun that is painted bright colours.