Borrowing by the Welsh Government does not appear to affect its Westminster block grant as long as it keeps within its borrowing powers limit. There is a general provision to meet a current shortfall in receipts from devolved taxes, thus:
The current borrowing powers of the Welsh Ministers are set out in section 121 of the Government of Wales Act 2006 as amended by the Wales Acts 2014. They may borrow funds from the UK Government for the purpose of meeting a temporary excess of sums paid out of the Welsh Consolidated Fund over sums paid into that Fund, any amounts it appears to them are required by them for the purpose of providing a working balance in the Welsh Consolidated Fund and any amounts which in accordance with rules determined by the Treasury are required by the Welsh Ministers to meet current expenditure because of a shortfall in receipts from devolved taxes, or from income tax charged by virtue of a Welsh rate resolution, against forecast receipts.
In addition there is a power, inserted by the Wales Act 2014, to borrow money from the UK Government for capital expenditure. There is a total borrowing cap of £1 billion on this borrowing, of which no more than £150 million can be borrowed annually.
Commercial lenders can also be a source for the capital expenditure borrowing.
https://senedd.wales/laid%20document...12846%20-e.pdf
https://law.gov.wales/constitution-g...erview&lang=en