Nickolo - I'm not getting into the other points, but
"the infraction is only committed AFTER you have signed the deal and not before."
You're wrong - For any transaction of property to be valid in BG, it must be notarised.
If you lie to the notary (about the price or anything else) then the transaction is not notarised correctly and your title to the property could be challenged.
OK that raises the issue of WHO could challenge it, and the only other party to the deal is the seller who has no more interest in challenging things than you do.
What I could forsee )but it would take a change in the law) is for the authoraties to be given power to challenge the transaction as "a person affected"
As the under declaration of price would result in lower taxes, the fraud has in effect caused the Revenue to suffer loss. On that basis they could challenge your ownership on that basis.
Next Question, is WOULD THEY? - probably not - it would be easier to seize the property under "proceeds of crime" legislation, once they had proven the fraud.
Finally, look at it politically - how would WE feel if Tony Blair said he was going to clamp down on fraud by people who live overseas, come to the UK, and avoid paying tax. - A sure vote winner
For that reason - it will come