Conservative MP Patrick Mercer, a former Army officer, said security and overseas aid were "inextricably linked".
He told BBC Radio 4's Today programme: "I absolutely understand the need for overseas aid although not necessarily at this level.
"But I do see that so much of the aid we have attempted to spend in the past in places like Iraq and Afghanistan has not been delivered as effectively as it might because of the lack of a benign security environment.
"If that means more money has to be spent on defence in order to increase the efficacy of overseas aid spending, I'm all for it."
Oxfam's head of policy Max Lawson told BBC Radio 4's Today programme the aid budget should be spent on "hospitals and not helicopter gunships".
The Prime Minister has said the government is considering spending money from the aid budget on peacekeeping and other defence-related projects.
Such a move would see millions of pounds being diverted from the Department for International Development to the Ministry of Defence.
Speaking to reporters on his way back from India, David Cameron said he intends to protect all £10 billion of Britain's aid budget, 0.7% of national income, but that he was "very open" to the idea of pooling resources between departments.
He said the money would comply with international aid spending rules and not be used for combat mission or equipment.
International Development Secretary Justine Greening said the UK ending financial aid for India in 2015 will save £200 million.
Britain will still pay India around £30 million after 2015 but this will be for "technical assistance".
Britain will continue giving India £280 million a year in financial aid until 2015, the Department for International Development has told ITV News.
After the aid grants have been phased out, Britain will provide "technical assistance" to the country, which will cost around £30 million a year.
The Department for International Development has announced the end of a lease on their London headquarters on the same day it said there would be no new financial aid to India after 2015.
Britain will no longer give India financial aid from 2015 but will in the future support areas like trade and investment and health.