To be fair - Peter does have a point.
However, I would expect that most GA pilots with a UK / JAA IR that learnt reasonably recently in the UK would have experience taking off on an IR flight plan in controlled airspace and being given to London Information to then get a clearance into controlled airspace or airways. All training from Bournemouth as an example would see this.
I do agree that for pilots who have an FAA IR that they would not really understand this (I certainly had the same issues when I first got an FAA IR). This is in no way a 'pop' at the FAA IR, more an observation that training that FAA training in the US doesn't really sjow you so much of the 'oddities' in the UK when taking off from a controlled airspace under IFR and going to London Information to then get a clearance into controlled airspace.