Peter Swallow, MP for Bracknell, said the decommissioned postbox on Windlesham Road in Priestwood has now been out of service for three months.
The box was removed as part of Royal Mail’s transition to digital postboxes, which has already led to replacements at two other sites in the area.
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Mr Swallow said: “Post boxes in Priestwood and across Bracknell Forest have been decommissioned without warning, and without proper notice or explanation for residents.
“This is completely unacceptable.
“I have written to the CEO of Royal Mail to get an urgent update and express my concern about how the transition to digital postboxes has been handled locally.”
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In a letter to Royal Mail’s interim CEO Alistair Cochrane, Mr Swallow raised concerns about the lack of communication and the timing of the removals.
He said: “I stressed my frustration that these post boxes had been removed just before Christmas, making it harder for residents to send post to loved ones over the festive period.
“Local councillors and I were not informed about the removal of these post boxes, and even when requested, Royal Mail were unable to provide a timeline for when the post boxes would be replaced.
“It is totally unacceptable that even after raising this issue with Royal Mail on multiple occasions, the situation remains unresolved.”
Mr Swallow called on Royal Mail to urgently replace the Priestwood postbox and improve communication with the public and stakeholders.
He said: “What steps will you take to ensure better communication with local residents and stakeholders as you roll out more digital post boxes, and more urgently, will you intervene to replace the Priestwood post box?”