Yes you can if you have someone willing to lend one to you, more than likely renting will give you a proper RIF.
Some sites like the one I regularly play at (Skirmish Airsoft Mansfield) have a store on site and will allow you to purchase a RIF as long as you leave the RIF at the site when not in use and they do expect that you plan on becoming a member of the site so you can get your UKARA membership.