I searched for How Not to Dal dy Dir by Izzy Wyn-Thomas in the British Library and National Library of Wales databases but they didn't seem to hold copies.
I think UK publishers have a statutory responsibility to deposit with the British Library copies of any of their publications within thirty days of them being published. The five other legal deposit libraries in the UK ,including the the National Library of Wales, are entitled to request copies too.
If anyone who has a reader's ticket to one of the six legal deposit libraries (London, Wales, Scotland, Dublin, Oxford and Cambridge) wants to see a copy of the book, I think it may be possible to request that the library gets hold of one for their collection. The Bodleian in Oxford, for example, says 'Where we identify a gap in our collection of British publications, our Legal Deposit Operations Office sends a claim to the Agency for the Legal Deposit Libraries (ALDL), which makes claims on behalf of all legal deposit libraries (except the British Library)'.