The former head of operations at the Royal Horticultural Society has pleaded guilty to three counts of trying to defraud the charity as part of a fraud plot worth a reported £700,000.
Stuart Medhurst, aged 54, appeared at Southwark Crown Court in London on Wednesday and pleaded guilty to one count of fraud by abuse of position and two of conspiracy to steal.
He will be sentenced next year after the conclusion of a trial of two alleged co-conspirators.
According to the Daily Mail newspaper, Medhurst, who left the RHS in 2013, conspired to steal nearly £700,000 from the charity over a 10-year period.
He had initially appeared at Westminster Magistrates’ Court in January alongside Shaheen Kadri and Elaine Summers, neither of whom worked for the charity, before the case was progressed to the Crown Court.
On Wednesday, Kadri and Summers also appeared at Southwark and pleaded not guilty to a single charge each of conspiracy to steal. Medhurst will be sentenced after the conclusion of their trial, which will begin 11 July 2016 and is due to last between five and seven days.
A spokeswoman for the RHS said in February that she was unable to confirm the amount of money involved, but said: "We can say that over the past three years we have been conducting in-depth audits across all our work and implementing more robust measures and controls to protect the society. Today we’re in a much stronger position to ensure unacceptable activity cannot take place within the society. Any losses to the revenue of the charity will largely be covered by insurance."
The charity, which works to "enrich everyone's life through plants and make the UK a greener, more beautiful place", according to its website, had 736 staff and an income of £71.9m in the year to 31 January 2014, down from £81.3m the year before, its accounts show.