* The Collected Poems of Gavin Ewart: This book, published by Carcanet Press in 2007, contains a comprehensive selection of Ewart's work, including "One Last Summer".
* The Gavin Ewart website: Although the website does not have the full text of the poem, it does list "One Last Summer" as one of Ewart's works, providing a link to where it was originally published.
* Other anthologies: It is possible that the poem was published in other anthologies of British poetry. You might find it listed in online databases like WorldCat, which provides information about library holdings.
You can also try searching online for the poem's title and author, although your search results may not be comprehensive due to the poem's limited publication.
Good luck in your search!