Inert items are NOT prohibited.
They are classed as 'restricted'
Weapons and ammunition: Sporting firearms and most ammunition can be admitted conditionally as import. All these articles are subject to domestic controls on possession of the firearms and import licensing requirements for imports into the United Kingdom.Items which give the appearance of being a prohibited weapon or explosive ordnance, even if incapable of being used as a weapon, will be subject to closer scrutiny which will cause delay; and will be transported by road, rail, or sea, rather than by air.
The above,taken from the RM website,seems to suggest that the items will be inspected (as happened to me!),and then allowed to progress through the system,albit not by air.
Cheers,
Andy