Ein cais ffurfiol ar gyfer cymhwysedd trethu yw’r tro cyntaf inni brofi’r system a daw’r cais ar ôl dwy flynedd o waith gan Lywodraeth Cymru i sicrhau bod gan Drysorlys Ei Mawrhydi wybodaeth ddigonol i asesu cynigion Llywodraeth Cymru. Mae’r profiad o symud drwy’r broses wedi bod yn hirfaith ac yn heriol, gyda Thrysorlys Ei Mawrhydi yn gofyn yn barhaus am fanylion ynglŷn â gweithrediad penodol y dreth arfaethedig – mater i Gymru – yn hytrach na gwybodaeth ynglŷn â datganoli cymhwysedd ar gyfer deddfwriaeth mewn maes trethu newydd. Ar 19 Awst 2020, ymatebodd Ysgrifennydd Ariannol y Trysorlys drwy ddweud y byddai angen mwy fyth o fanylion cyn y gellid bwrw ymlaen â’n cais ffurfiol.
Our formal request for tax competence is the first time we have tested the mechanism and the request follows over two years of work by Welsh Government to ensure HM Treasury had sufficient information to assess Welsh Government proposals. The experience of moving through the process has been protracted and challenging, with HM Treasury continually requesting detail related to the specific operation of the proposed tax – a matter for Wales - rather than information related to devolving competence for legislation in a new area of taxation. On the 19 August 2020, the Financial Secretary to the Treasury responded by stating that yet more detail would be required before our formal request could be taken forward.