Search the theme source-code for SITE_HOME_URL and try replacing it with WP_HOME or with the result of esc_url(home_url()). Locate THEME_PATH and replace it with the result of get_theme_root().
EDIT: In the case of expressduplication.co.uk/SITE_HOME_URLspecial-offers there is probably a wp_redirect() or wp_safe_redirect() that doesnt work because of the undefined constant SITE_HOME_URL.