Tearfund chief executive Matthew Frost says he is "bitterly disappointed" that the Government has failed to follow through on its pledge to commit 0.7% of national income to aid.
Although the promise is in the coalition agreement, it was left out of the Queen's speech today.
Reacting in a statement, Mr Frost said people had a responsibility to "look out for each other".
"Charity begins at home but it doesn't stay there. A strong family is generous to each other and to their neighbours and so it's here in our own country that we must learn to look out for each other and share whatever we can with those in need, here in the UK and overseas," he said.
"That's why the government should have honoured their promise to legislate for 0.7% of our country's income to help people in poor communities find their own ways out of poverty and build their families and communities to be strong, resilient and productive.
"I'm bitterly disappointed that we didn't hear that promise fulfilled today."
ActionAid's head of advocacy Melanie Ward said the development would make it harder for countries receiving UK aid to plan ahead.
"The aid budget is a tiny proportion of Britain's national income," she said.
"Having it enshrined in law would provide poor countries with the certainty they need to plan their development and deliver the best value for money from UK aid."