vat-validation-regex

at, /^ATU[A-Z0-9]{9,9}$/,
be, /^BE[0-9]{10,10}$/,
bg, /^BG[0-9]{9,10}$/,
cy, /^CY[A-Z0-9]{9,9}$/,
cz, /^CZ[0-9]{8,10}$/,
de, /^DE[0-9]{9,9}$/,
dk, /^DK[0-9]{8,8}$/,
ee, /^EE[0-9]{9,9}$/,
el, /^EL[0-9]{9,9}$/,
es, /^ES[A-Z0-9]{9,9}$/,
fi, /^FI[0-9]{8,8}$/,
fr, /^FR[A-Z0-9]{2,2}[0-9]{9,9}$/,
gb, /^GB[0-9]{9,9}$|^GB[0-9]{12,12}$|^GBGD[0-9]{3,3}$|^GBHA[0-9]{3,3}$/,
hu, /^HU[0-9]{8,8}$/,
ie, /^IE[A-Z0-9]{8,8}$/,
it, /^IT[0-9]{11,11}$/,
lt, /^LT[0-9]{9,9}$|^LT[0-9]{12,12}$/,
lu, /^LU[0-9]{8,8}$/,
lv, /^LV[0-9]{11,11}$/,
mt, /^MT[0-9]{8,8}$/,
nl, /^NL[A-Z0-9]{12,12}$/,
pl, /^PL[0-9]{10,10}$/,
pt, /^PT[0-9]{9,9}$/,
se, /^SE[0-9]{12,12}$/,
si, /^SI[0-9]{8,8}$/,
sk, /^SK[0-9]{10,10}$/

These are the correct rules at the time of creation (29/04/2016), feel free to comment if something is not right or to add a country