Mae hi wedi dod i’r amlwg nad yw’r broses y cytunwyd arni ar gyfer datganoli cymhwysedd trethu pellach i Gymru yn addas i’r diben, ac o safbwynt ymarferol mae’n nodedig o debyg i broses flaenorol y Gorchmynion Cymhwysedd Deddfwriaethol. Gwaethygir y sefyllfa gan y ffaith y gall Trysorlys Ei Mawrhydi symud y pyst o ran pa wybodaeth sydd ei hangen ar unrhyw adeg. O ystyried yr heriau yr ydym wedi’u hwynebu wrth hebrwng y maes penodol a chul iawn hwn o gymhwysedd deddfwriaethol drwy’r system, mae’n anodd rhag-weld sefyllfa lle gallai Llywodraeth Cymru lwyddo i ddadlau’r achos dros gymhwysedd trethu pellach, os bydd dull gweithredu Llywodraeth y DU yn parhau. Bydd methiant y system hon yn cael effaith sylweddol ar allu’r llywodraeth hon a llywodraethau’r dyfodol i ddefnyddio treth fel ffordd o ddylanwadu ar ymddygiad neu gefnogi gwariant cyhoeddus i ddiwallu anghenion pobl Cymru.
It has become clear the agreed process for devolution of further tax competence to Wales is not fit for purpose, and in practice bears a striking similarity to the previous process of Legislative Competence Orders. This is compounded by the fact HM Treasury are able to move the goalposts as to what information is required at any point. Given the challenges encountered taking this particular, very narrow area of legislative competence through the mechanism, it is difficult to envision a scenario whereby, with the current UK Government approach, the Welsh Government could successfully make the case for further tax competence. The failure of this mechanism significantly impacts the ability of this government and future governments to use tax as a lever to influence behaviour or support public spending to meet the needs of the people of Wales.