▁Convention , ▁which ▁draft ed ▁the ▁Constitution al ▁Tre aty ▁for ▁the ▁European ▁Union . ▁Following ▁the ▁failure ▁of ▁the ▁rat ification ▁process ▁for ▁the ▁European ▁Constitution , ▁the ▁clause ▁was ▁incorpor ated ▁into ▁the ▁Tre aty ▁of ▁Lis bon ▁which ▁entered ▁into ▁force ▁in ▁ 2 0 0 9 . ▁ ▁Prior ▁to ▁this , ▁no ▁provision ▁in ▁the ▁treat ies ▁or ▁law ▁of ▁the ▁EU ▁out lined ▁the ▁ability ▁of ▁a ▁state ▁to ▁volunt arily ▁withdraw ▁from ▁the ▁EU . ▁The ▁absence ▁of ▁such ▁a ▁provision ▁made ▁withdraw al ▁techn ically ▁difficult ▁but ▁not ▁impossible . ▁Leg ally ▁there ▁were ▁two ▁interpret ations ▁of ▁whether ▁a ▁state ▁could ▁leave . ▁The ▁first , ▁that ▁so ver eign ▁states ▁have ▁a ▁right ▁to ▁withdraw ▁from ▁their ▁international ▁commit ments ; ▁and ▁the ▁second , ▁the ▁treat ies ▁are ▁for ▁an ▁un limited ▁period , ▁with ▁no ▁provision ▁for ▁withdraw al ▁and ▁calling ▁for ▁an ▁" ever ▁closer ▁union " ▁– ▁such ▁commit ment ▁to ▁un ification ▁is ▁in compatible ▁with ▁a ▁un il ater al ▁withdraw al . ▁The ▁Vienna ▁Convention ▁on ▁the ▁Law ▁of ▁Tre aties ▁states ▁where ▁a ▁party ▁wants ▁to ▁withdraw ▁un il ater ally ▁from ▁a ▁treat y ▁that ▁is ▁silent ▁on ▁se cess ion , ▁there ▁are ▁only ▁two ▁cases ▁where ▁withdraw al ▁is ▁allowed : ▁where ▁all ▁parties ▁recogn ise ▁an ▁inform al ▁right ▁to ▁do ▁so ▁and ▁where ▁the ▁situation ▁has ▁changed ▁so ▁dr ast ically , ▁that ▁the ▁oblig ations ▁of ▁a ▁sign atory