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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The parents of Dylan Seabridge, from Pembrokeshire, said they believed their son was suffering from growing pains.
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An inquest is to be held into the deaths of four family members who died when their car was involved in a crash near Aberystwyth in June.