Mischief PR was briefed to raise awareness of Project Neptune, through which the conservation charity now protects 775 miles of British coastline.
The agency found a poem that had been gifted to the National Trust by John Betjeman to help raise funds in the archives, which triggered the idea for the campaign. John Cooper Clarke was commissioned to write a new poem about what the coast means to the UK.
The first few verses of the poem were unveiled in a TV ad, developed by the trust's advertising agency, 18Feet & Rising.
Mischief's idea was that the poem would become 'The Nation's Ode to the Coast', and it asked the general public to submit their contributions about why they love the coast.
More than 11,500 people submitted their thoughts via the #lovethecoast hashtag, by sending postcards, emails and letters. A total of 17 people were chosen to appear in the final cut to recite lines from the poem.
To date, the campaign has achieved 300 pieces of media coverage and more than 500,000 views of the video, Mischief said.
Robin Lewis, senior marketing manager at the National Trust, said: "The PR, social and paid campaign will finish at the end of October but we already have some strong indicators of success. The Coast campaign coverage has shown some great scores on increasing warmth towards the National Trust and its relevance to our target audiences. There's been fantastic social media engagement and, of course, more than 14,000 contributions from the public. The reception to the final poem has been really positive.
"Our future brand marketing approach will focus on further explaining the National Trust's work caring for special places for ever."