I live in Wales, can I go on holiday in Wales or the rest of the UK?
No. Travelling within Wales for a holiday is not one of the permitted reasons to travel under the Regulations. It is also not a reasonable excuse to travel to the rest of the UK for a holiday during the firebreak period.
Maybe that will change after the Welsh lockdown is finished but then anyone from Wales would then fall under a English law when they cross the border.
This 4 nation approach shows the perils of devolved power. You just need to look at Spain to see how it doesn’t work particularly with their Covid response