Up to 125 jobs could go at Royal Botanic Gardens Kew because the organisation faces a shortfall of £5m for its 2014/15 budget, the charity has said.

The shortfall arose because of a combined reduction of around £3.5m from its two main grant sources, a grant-in-aid from Defra and from the Kew Foundation, which raises money from supporters, a charity spokeswoman said today. At the same time the organisation experienced “unavoidable cost increases” of roughly £1.5m.

RBG Kew plans to fill one-third of the funding gap by growing its “self-generated” income but said costs also needed to be reduced. The number of visitors to the site increased by 29 per cent last year.

RBG Kew currently employs around 750 people on its main site and at its sister gardens Wakehurst Place in Sussex.

In a statement a spokeswoman said: “RBG Kew is driving hard to grow self-generated income, and we aim to fill roughly a third of the shortfall next financial year through income growth. RBG Kew is also working to make the organisation more efficient. Costs will be reduced and these will include changes in staffing.

“We will be working with staff to explore all options including schemes for voluntary exits, reduced working hours and unpaid leave, before moving onto consideration of redeployment, voluntary redundancies or, as a last resort, compulsory redundancies.”

RBG Kew will share more detail once it has completed the internal process.