Britain must accept a less interventionist role in the world and review defence spending to address "extreme pressures" on budgets, opposition Conservative foreign affairs spokesman William Hague will say on Tuesday, Reuters reported.
In a speech setting out Conservative foreign policy aims, Hague will say Britain can no longer tell other countries how to govern themselves but can, and should, exert its influence when necessary.
The Conservatives, well ahead of the Labour government in opinion polls with less than a year to go before an election, are starting to flesh out how they might govern Britain.
"As a nation we will have to accustom ourselves to there being more situations which we dislike but cannot directly change," Hague, who is likely to become foreign minister in any Conservative government, will say in a speech in London.
"But it is our contention that Britain must seek to retain her influence wherever possible and in some places seek to extend it."
Britain has sent thousands of troops to both Iraq and Afghanistan in recent years, putting its armed forces and its defence budget under great strain. Most of its troops have now left Iraq, though it still has 9,000 in Afghanistan.
Hague said Britain should not shy away from "rigorous debate" with its close ally, the United States, and should push for western Balkan states and Turkey to join the European Union as soon as possible.
More effort should be made to improve relations with "friendly Muslim nations" -- even those which may not share Britain's democratic or social values.
"It is a vital part of understanding the world we are facing in the coming decades that we will not be able to prescribe the form of government in all the countries with whom we need friendly relations," he will say.
Hague will say his party would conduct a wide-ranging strategic defence review, if elected, to better address the tighter departmental budgets that any government will need to impose to help tame record-high public borrowing.
"It will be a defence and national security review, covering all aspects of Britain's security and not just the armed forces," he will say.
"It will be guided by the requirements of foreign policy and not solely by financial constraints, and we will not shrink from adapting our future armed forces for this changed world."
The Labour government has said it also plans to launch a strategic defence review next year.
Britain's strategy in Afghanistan, an intervention the traditionally hawkish Conservative party supports, has been brought into question after a surge in British casualties raised concerns about troop levels and equipment standards.
The Conservatives, in opposition since 1997, laid out plans for regulating the financial sector this week, including the abolition of the Financial Services Authority and putting the Bank of England in charge of financial stability.