I would never disagree with Fuji who I know is a specialist on this, whereas I am a mere victim, but would like to point out that the Revenue will hit what they ritually regard as a dodgy business and it is then up to the proprietor to prove his innocence.
This is expensive, and even dealing with a long enquiry (the Revenue love nothing more than a long dreary enquiry) will cost an absolute minimum of 4 digits and easily 5 digits.
The question is whether it's worth doing.
On a 1970s spamcan, no. On a £300k IFR tourer or above, yes, but I would do the Denmark route, and keep Customs out of the whole setup. There is still a nice fat fee to the Danish lawyer who clearly needs substantial compensation for injury as a result of falling over as he laughs all the way to his bank, but the saving is well worth it.
In comparison, my personal experience of C&E has been nothing but professional. This I find curious since they have much greater powers than the Revenue.