zoopla.nextpagekey.user.js

// ==UserScript==
// @name        Keyboard Page Switcher - Zoopla
// @namespace   nextpage.zoopla
// @description Allows the use of keyboard navigation keys to switch between pages on Zoopla
// @include     https://www.zoopla.co.uk/*
// @version     1.0.0
// @grant       none
// ==/UserScript==

"use strict";

window.onkeyup = function(e) {

    if (document.activeElement.type !== "text") {

        var key = e.keyCode ? e.keyCode : e.which;

        if (key == 37) {
            document.location = document.getElementsByClassName("paginate")[0].children[1].href;
        }
        else if (key == 39) {
            var paginateElementChildren = document.getElementsByClassName("paginate")[0].children;
            document.location = paginateElementChildren[paginateElementChildren.length - 1].href;
        }
    }
}

console.log("Keyboard Page Switcher (Zoopla) active");