Inventor Sir James Dyson is giving £500,000 to the appeal to build a new baby care unit in Bath.

The donation from the businessman whose career began in Bath has given fundraisers at the Forever Friends Appeal the confidence to give the go-ahead for building work to begin.

The James Dyson Foundation, set up by Sir James and his wife Lady Deirdre Dyson, will be ploughing the money into the planned new neonatal intensive care unit at the Royal United Hospital.

It is the single biggest donation ever received by the appeal, which has set up the Space to Grow campaign to fund the new unit to replace existing cramped facilities for premature and sick babies.

The donation means that the campaign has now reached its last 15 per cent of the fundraising, with just £900,000 to go.

In recognition of the foundation's support the unit will be known as The Dyson Centre for Neonatal Care.

Appeal chairman John Cullum said: "This is an amazing boost to our campaign, enabling the RUH to press the go button to begin the building work."

He said the appeal team was now better placed to raise the final £900,000 within the next few months, with the foundation money coming hard on the heels of increased funding from the RUH NHS Trust for the project.

"We are pleased to say that this very substantial donation follows increased RUH capital investment, acknowledging their commitment to this groundbreaking project, and taking the pioneering ambitions for this innovative sustainable building a huge step closer to completion.

"I would like to express my sincere thanks on behalf of the appeal and the project team to James and Deirdre Dyson and the James Dyson Foundation.

Architects from Bath firm Feilden Clegg Bradley Studios have been working with nurses and clinicians to design a building housing 21 cots using sustainable materials.

Their aim is to come up with an environmentally-friendly unit providing a holistic model of care which will be a model for future NHS buildings.

Sir James, who was given his first break at Bath firm Rotork and who had wanted to set up a design school in the city, said the unit's principles reflected the aims of his foundation, an educational charity supporting science, design and engineering.

He said: "This new unit will improve the care of babies that need medical support and provide more intimate surroundings for their parents.

"As an engineering project, it will lead the way in environmentally sustainable hospital development, and set an example for others to follow.

"Along with the trustees of The James Dyson Foundation, I look forward to seeing the building work start."

The Dyson support started with an initial £50,000 donation, part of which enabled the appeal to fund a feasibility study.

Lady Dyson was today visiting the existing NICU to hear about plans for the new unit.

She will be able to see the new site, which builders have started to clear in preparation for work to begin.

The appeal will now be raising the last tranche of money from a range of sources including individual donations, corporate supporters and public events.

Mr Cullum said: "The RUH is all ready to get the build under way to ensure that the urgently needed new unit opens as soon as possible.

"In the mean time the appeal is still busily continuing its fundraising but really do need people's tremendous support to help us bring the campaign to a wonderful conclusion over the next few months."

For more information on the appeal, visit www.foreverfriendsappeal.co.uk/nicu.