Yes, you are okay to use a RIF at an airsoft skirmish, it isn't illegal to own one (or as many as you like in fact), but bizarrely, it is illegal for someone to supply one to you if you are not going to use it for airsoft skirmishing at a recognised airsoft skirmish site which has insurance for that purpose (which you are going to do, so that's fine and perfectly legal). In practice however, even if you were not gonna go skirmishing with it, who would ever know where you got it from? In other words, don't worry about that too much, there is no such thing as a licence for an airsoft weapon, they don't require one. So...
The golden rule here, is basically don't be a dick with the thing. Cover it up when transporting it to and from the airsoft skirmish, and make sure it is unloaded and any battery or other power source it uses is not fitted when you do transport it, so it can't actually be fired whilst you are in the process of going to and from the airsoft site. If you drive, stick it in the boot of your car, or if it is a hatchback or whatever, with no boot, then cover it up when it is in the back of the car. If you don't drive, and are going on a bus or a train or walking any appreciable distance with it, then put it in either a box or a bag of some kind, and the less this looks like a rifle case, the better (soft material electric guitar cases are good for that purpose, and most guitar shops will have them for about a tenner).
As long as you don't behave like a dick with an airsoft weapon, firing it over a neighbours fence or waving it about in the street or other stupid things like that, and only use it for skirmishing at an airsoft site, then you are fine.
It's worth anyone who is into airsofting to get familiar with the laws on having, owning, making, modifying and using airsoft weapons. Most people on here won't steer you wrong if you ask about that stuff, but don't rely on 'this bloke on such and such a forum told me the law said, this was okay...' know the law for yourself, do a search on google for the VCR Act and look at Sections 36 and 37 of it, which are the bits pertaining to airsoft. You will see that you are fine, but more importantly, you will actually know that you are fine.
