Studies made for EU reveal that the VAT Gap (difference between theoretical VAT receipts and actual payments) exceeds 100BN€ every year since 2000 (118,8bn€ in 2009). All of this is not fraud or loopholes - there can be legal exceptions. In any case it is
our money - something we tax payers should be interested in getting paid (to get lower salary taxes etc).
The gap varies between 1% (Luxembourg) and 30% (Greece).
The most efficient way of getting the fraudulent and loophole parts under control is to migrate from paper based invoicing to e-invoicing and collect the VAT in connection with invoice payments (split payment as described in earlier posts here).
More:
http://ec.europa.eu/taxation_customs/resources/documents/taxation/tax_cooperation/combating_tax_fraud/reckon_report_sep2009.pdf