The bridge provides a crossing point between Anglesey and mainland North Wales.
Phase two of the maintenance works, which entail full repainting and other preservation activities, were planned to begin two years ago.
But a potential defect with the hangers was discovered, which forced their immediate replacement (phase one) and subsequently postponed the phase two works until after the hangers were replaced.
The phase one works were completed last October and permitted the bridge to re-open to all traffic during the winter period.
But due to procurement issues, additional requirements and issues in gaining necessary licenses, phase two is now scheduled for next spring.
Welsh Government’s transport secretary, Ken Skates, said: “This will result in the works continuing during the bridge’s actual 200th anniversary date of January 30, 2026, which is not what we would have wanted.
“However, UK Highways A55 Ltd have committed to us that they will ensure they are completed for the summer period to ensure the celebrations, which are currently planned to coincide with Thomas Telford’s Birthday on August 9, 2026 at the height of the tourist season, can go ahead without restrictions and the bridge will be returned to its full former glory.
“My officials will be monitoring the work closely, through frequent site visits and regular meetings with the site team, and if there is any scope for the work to be finished earlier, then it will be done.
“I am extremely disappointed that the original programme from UK Highways A55 DBFO Ltd is now delayed.
“We were given assurances at the time that the phase two works would be completed by December 2025, and I know this news will be very disappointing for the community and others.
“The age of the bridge and the fact it’s a critical asset to the area means that it is imperative that works are completed to the highest of standards to ensure it continues to operate for the next 200 years.”
Rhun ap Iorwerth, Ynys Môn MS, said: “This is a huge blow for the local community, its economy and Ynys Môn more widely.
“The Welsh Government promised that the work would be complete before the 200th anniversary of the bridge in January 2026, but now the planned celebrations by local community groups will have to be put on hold.
“Businesses will be counting the cost, commuters will suffer yet more delays for longer, and there’s also the prolonging of safety concerns regarding access on and off the island in emergency situations.
“I have raised concerns with UK Highways that seemingly little maintenance work was actually being carried out on the bridge.
“Regrettably, they have kept residents in the dark and the fact that Welsh Government has announced this news on a Friday afternoon means there is no opportunity to ask the many questions residents will have.
“This announcement, coupled with the difficulties many on Ynys Môn faced over the Christmas period with the temporary closure of Holyhead Port, is further proof that the Labour Welsh Government is not serious about making sure our island infrastructure is fit for the 21st century.
“I will be raising this matter on the floor of the Senedd at the earliest possible opportunity, and will continue to make urgent enquiries.”