All 1,800 firms listed on the London Stock Exchange's Main Market will be required to list their greenhouse-gas emissions from next April, British Deputy Prime Minister Nick Clegg said at the Rio+20 summit on Wednesday.

The move means that Britain will become the first country to make it compulsory for companies to include emissions data for their entire organizations in their annual reports.

At a side event at the UN Conference on Sustainable Development, Clegg said that the reporting would help corporations and investors identify potential areas of savings that can be made through energy efficiency.

"Counting your business costs while hiding your greenhouse gas emissions is a false economy," he was quoted as saying in a statement issued by Britain's environment department.

"British companies need to reduce their harmful emissions for the benefit of the planet, but many back our plans because being energy-efficient makes good business sense, too.

"It saves companies money on energy bills, improves their reputation with customers and helps them manage their long-term costs, too."

The regulations have been under discussion between government and business for months.

They will be introduced from the start of the next financial year in April and be reviewed in 2015, pending a decision whether the requirement should be extended to all large companies from 2016.