Nick Hurd is the Member of Parliament for Ruislip, Northwood and Pinner. Zac Goldsmith is the Member of Parliament for Richmond Park.

Page 97 of the Budget Red Book is not where one instinctively looks for inspiration if you are concerned about protecting the natural world. However, in declaring the intention to designate the pristine oceans around the tiny island of Pitcairn as a Marine Protected Area, we believe that the Chancellor has delivered the single biggest conservation measure taken by any Government ever. And it will be done at a very small cost.

This is important. While the focus of much of the green debate in recent years has been around climate change, a disaster has been unfolding in the world’s oceans.

A study published in Science predicts that, on current trends, all of the world’s fisheries will have collapsed by 2048. Meanwhile, it is estimated that nearly 90 per cent of all large fish are gone .The problem is a combination of lawlessness in the high seas, wholesale destruction of the key breeding grounds for fish, and tools used by the giant operators that are irreconcilable with a sustainable future. The biggest vessels today use long lines that stretch over sixty miles, and nets big enough to engulf two Millennium domes.

Purely in terms of the great loss of biodiversity this is a tragedy. But it is a humanitarian issue too. Nearly a billion people depend on fish as their primary source of protein, and nearly a quarter of a billion depend on fish for their livelihoods. The food security implications are self-evident, but so too are conventional security concerns. For example, it is clear that piracy grew rapidly in Somalia after the seas were declared a dead zone.

The easiest, cheapest and quickest solution is the creation of protected areas. There is no question that they work. Spain has an appalling record when it comes to fishing, but catches close to the country’s first MPA, the Tabarca Marine Reserve, were 85 per cent higher than elsewhere after just 6 years of protection.

Governments have already agreed an international target of protecting 10 per cent of coastal and marine areas by 2020, but, as is so often the case with grandiose declarations, very little progress has been made.

We should be proud that Britain has now shown genuine leadership. We still control some 6.8 million kilometres-squared of ocean, the vast majority of which is within the UK Overseas territories, which harbour 90 per cent of UK’s biodiversity.

We have made some progress already, when the British Indian Ocean Territory was turned into what was then the world’s largest fully protected marine reserve in 2010.

But with this Budget announcement, we have taken another giant step. The Pitcairn Islands in the South Pacific are famous because their inhabitants are descendants of Fletcher Christian and his fellow mutineers on the Bounty and their Tahitian companions. It is perhaps the remotest inhabited area on earth, impossible to access except by boat. For the time being, the oceans around Pitcairn are clean and abundant. It has some of the best coral reefs in the world, intact deep sea habitats and countless species new to science.

With the giant ocean trawlers fast approaching, today’s announcement – endorsed by all of the island’s inhabitants without exception – could not be more timely. The new Pitcairn reserve will be the world’s largest single fully protected area.

We have campaigned on this issue, alongside other Conservative colleagues, for a while. So we strongly welcome this move, but our hope is that this is just a start. There are more protection opportunities that must be seized. Pitcairn is not our only large ocean territory. We can and should be looking to do something similar around Ascension Island, if there is agreement from the people on the island.

David Cameron said he wanted to “lead the greenest Government ever”.  This aspiration has been hard to live up to. It has attracted inevitable cynicism. However, the track record deserves more respect. We are clearly leading the world in protecting the oceans. On the land, we have planted more than 11 million trees, and are now expanding England’s woodland cover at a rate that hasn’t been seen since the fourteenth century. In the face of the carbon challenge, we set up the ground breaking Green Investment Bank, and renewable energy capacity has doubled on our watch.

We see today’s announcement as building on a long legacy of Conservative achievement in protecting the natural environment. Duncan Sandys introduced the Clean Air Act. Margaret Thatcher was the first world leader to take Climate Change seriously, and with John Gummer ensured that the Montreal Protocol, designed to tackle substances that deplete the precious ozone layer, was fit for purpose. And now a Conservative-led government has taken a huge step on the road back to sanity and responsible duty of care to the oceans we depend on. This is something that Conservative candidates should take pride in.