I think a big reason that many IMC holders would not wish to go ahead and 'demonstrate their skills' to get an IR currently, is the sheer amount of unecessary money to be sent to the numpties at Gatwick for doing...pretty much nothing. 700 pounds for the privelige of taking a short examination? The CAA certainly monopolise their way to impressive hourly rates for sitting on their arses and trying to stop us from flying!
What do they even do nowadays? All the recent times I have sent them questions, I've received the reply 'we don't know, ask EASA'.