Andy Furey is the National Officer for Communication Workers Union, which represents staff working in Crown Post Offices.
He told ITV News: "A Welsh town like Holywell needs a Crown Post Office. If we lose it, this could be the death knell for the high street in Holywell."
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Two families involved in supplying drugs and money laundering in north Wales have been convicted.
More rain for Wales on the way over the next few days.