The Conservatives will publish all government contracts worth more than £25,000, the party's leader is to promise today.

David Cameron wants the details of deals to be published in full from January 2011, including all performance indicators, break clauses and penalty measures.

In a speech he will make to the Technology, Entertainment, Design (TED) conference in California today, he will argue that laying bare such detail will allow the public to identify wasteful spending and give smaller businesses a better chance of winning government contracts.

Scrutiny of public-private sector contracts is often frustrated because commercial confidentiality concerns prevent public bodies from revealing the full details of arrangements.

Cameron's pledge comes as shadow defence minister Liam Fox and shadow transport secretary Theresa Villiers ask the government to delay the completion of a private-finance contract to replace the Sea King helicopter fleet used in search and rescue operations.

The Ministry of Defence has chosen Soteria as its preferred bidder, and defence minister Quentin Davies has announced that the government wants to conclude a contract this year.

However, Fox and Villiers want the decision to be put off until after the election because of concerns about what the contract detail will say about penalties and let-outs in the case of performance failure.

In a joint statement, they said: "We are not opposed to the principle of contracting out - part of the search and rescue service already is - but we are deeply concerned that a project of this importance and magnitude should be rushed through in the teeth of a general election.

"Given the government's record on PFIs, and its performance on helicopter contracts especially, we will want if elected to look at the fine details of the contract.

"One key area is the levels of penalties - and the let-outs - for performance failure. Lives are at stake."