The conservation charity WWF-UK’s income went up by 15 per cent to £66.2m in 2011/12.
Its latest accounts, which cover the year to the end of June 2012, show that part of the increase was down to a donation of nearly £4.8m from the Rufford Foundation towards the charity’s new £20m offices in Woking, Surrey, which are under construction.
The gift helped the charity’s overall income to rise from £57.7m in 2010/11 to £66.2m. Membership and donations from individuals increased from almost £28.7m to £31.8m.
A capital fund set up to cover the costs of the new headquarters has accrued £5.5m in total, including the £4.8m donation.
A spokesman for the charity said the remainder of the cost of the new building would come from funds raised by private donations and a mortgage.
The charity will move from its existing headquarters in nearby Godalming, which has been its base for more than 20 years.
The new offices, dubbed "the living planet centre" by the charity, received planning permission in February 2011 and are expected to open in the second half of the year.
Designed by Hopkins Architects, the firm behind the velodrome at the Olympic Park in London, the new centre, covering 4,000 square metres, will be surrounded by greenery, with shrubs, trees and flowers around the car park.