You can be sent a RIF declaration for a package that has not been looked at - an early question would be “Does it contain a RIF?”, so your answer is “No”, the same answer if asked “Does it contain an IF?”
If it were a RIF you don’t necessarily need UKARA as the legal requirement is one of the VCRA Defences - UKARA is the easiest to import with as it is the most commonly recognised
As mentioned, some forms may as about “RIF parts”, that is not a requirement under VCRA - however it was a so called “solution” of certain overseas Airsoft shops to sell RIFs for delivery in multiple packages, or in other words - smuggling through customs
You can choose to say yes to RIF parts and if they have included that question they will have another to justify that you are not planning a VCRA offence of manufacturing a RIF / modifying IF to RIF without a defence. As long as are not doing that then pre-plan for your alternative non UKARA defence - if you can’t think of a way to justify that on a form for the import then consider the risk of your £
