The two charities already share office space and run joint events. A joint statement yesterday said: "The two umbrella bodies that represent grant-making trusts and foundations in the UK have agreed to start talks on how they can collaborate further to improve support services to their members.
"Building on a history of close joint working, ACF and ACO have agreed to explore ways of enhancing our membership offers and strengthening voice and representation for our respective sectors. Our two boards will be looking more closely at opportunities for collaboration over the summer, prior to reporting on progress in October.
"No details are available on the outcome of discussions, which are at an early stage."
Carol Mack, deputy chief executive of the ACF, and Dominic Fox, chief executive of the ACO, both declined to comment further on the statement and whether or not the talks would lead to a merger.
The ACF has 10 staff members, a membership of 330 and an annual turnover of £800,000. The ACO consists of two employees, 140 members and an annual turnover of £87,057 in the year to September 2010.
"The ACO has done a lot of work in the past 12 months to improve its support to members," said Fox. "This is an opportunity to continue and develop the support on offer."