Gallai cytundeb masnach rydd â'r UE a fyddai'n debyg i'r cytundeb diweddar â Chanada arwain at leihad o tua 6% yn yr economi. Yn ôl gwaith dadansoddi, byddai hyd yn oed alinio polisi'n agos â'r UE drwy fod yn aelod o'r Ardal Economaidd Ewropeaidd (EEA) yn gallu arwain at leihad o tua 2% i 4% yn yr economi na fyddai wedi digwydd fel arall.
A free trade agreement with the EU along similar lines to the recent agreement with Canada could result in the economy being some 6% smaller. Analysis also shows that even close alignment to the EU in the form of EEA membership could result in the economy being some 2% to 4% smaller than would otherwise have been the case.