David Cameron has written to the National Trust reassuring it over plans for shaking up the planning system.
The Prime Minister said new laws were designed to "achieve a balance" between the environmental, social and economic dimensions of developments.
He said the "beautiful British landscape is a national treasure" and expressed determination to protect the "magnificent countryside".
"Poorly designed and poorly located development is in no-one's interest," Mr Cameron wrote.
The Prime Minister's views were disclosed publicly for the first time in the missive sent on Monday night. The Trust has been leading a campaign to oppose the reforms, which are currently the subject of consultation.
Mr Cameron's letter, seen by The Daily Telegraph, reads: "Let me say at the outset that I absolutely share and admire your commitment to the countryside, and wholeheartedly agree that policymakers have an enormous responsibility to our environment.
"Both as Prime Minister, as a rural constituency MP, and as an individual, I have always believed that our beautiful British landscape is a national treasure. We should cherish and protect it for everyone's benefit."
Ministers are pushing through plans to replace more than 1,000 pages of planning regulations with just 52 in the National Planning Policy Framework.
The change is controversial because it writes into the rules a "presumption in favour of sustainable development".
Campaigners fear swathes of England could be concreted over as urban sprawl gathers pace.