The funding from the Department of Health and Social Care follows a £20 million investment awarded last year and will support the hospital’s redevelopment programme.
The scheme centres on a new six-storey building at Wycombe Hospital, which is set to provide facilities for cardiology, stroke and theatre services, alongside a significant expansion of endoscopy services.
Buckinghamshire Healthcare NHS Trust said the project is intended to support its long-term ambition of moving services out of the ageing Wycombe Tower Block.
Groundworks are currently taking place across the footprint of the new building and are due to be completed by the end of the year.
The next major phase of construction is expected to begin in January when structural steelwork is installed, bringing the development above ground for the first time.
The trust said the additional funding will allow it to continue detailed planning and design work for future phases of the redevelopment while construction of the new facility progresses.
Raghuv Bhasin, chief executive of Buckinghamshire Healthcare NHS Trust, said: “We are delighted to receive this additional £25 million investment from the Department of Health and Social Care.
“This funding is a strong vote of confidence in our plans to transform healthcare facilities at Wycombe Hospital and create a modern environment for patients, families and colleagues.
“The redevelopment represents a once-in-a-generation opportunity to improve healthcare facilities for Buckinghamshire residents.
“This additional funding enables us to continue making progress while developing plans for the next stages of the programme.
“Construction work is moving forward well and it is exciting to see our vision beginning to take shape on site.”
The first phase of the development is set to provide a new endoscopy unit.
The trust said planning and design work for future phases is continuing, with discussions ongoing with NHS England and national partners over the wider funding programme needed to deliver the full redevelopment vision for the site.
Buckinghamshire Healthcare NHS Trust provides acute hospital and community healthcare services for people across Buckinghamshire and surrounding areas.
The trust cares for more than half a million patients each year and employs over 7,000 staff.
Its hospitals include Wycombe Hospital and Stoke Mandeville Hospital, which is home to the internationally recognised National Spinal Injuries Centre.