The VCRA was brought in to deal with a raft of issues that were prevalent at the time, one of which was 'springer kiddies' (young kids running around with realistic looking springer pistols and pointing them at people causing all sorts of headaches for the local Police ARUs).
Whilst is does seem a waste of time the VCRA has reduced the incidents of kids running around with realistic looking guns in public.
As already pointed out, you do not need a valid defence to own a RIF, but you need a valid defence to buy one or, more accurately, you need to provide a valid defence to the retailer, as it would be the retailer that would be committing the offence.
If you modify an imitation firearm so it becomes a realistic imitation firearm then you are committing an offence unless you have a valid defence.
One of the easiest ways of demonstrating you have a defence is a UKARA membership.
Sitting Duck puts it in a very common sense way - don't be a dick. Many years ago the 'standard' advice on carrying your weapons to and from a skirmish was simple - weapon goes in a case or bag, is transported without batteries or gas in situ and is transported with magazine removed - preferably stored in a separate pouch. If stopped by the Police inform them what you have in the bag / case (toy gun) and ask them if they want you to open it.
In the real world there will be very few Police Officers who will know the in's and out's of the VCRA in relation to the IFs and RIFs, so unless you are being an idiot you are not likely to attract their attention.
