links in template outputting as .html instead of .php

In some of my templates, I have a relative link to a booking page. The link is ...booking.php but when the page is viewed in the browser and the link clicked, it sends me to booking.html and a 404 error.

Template code:

<perch:if exists="clinic1_bookings"><perch:content id="clinic1_bookings" type="textarea" label="Clinic 1 Bookings Text" help="OPTIONAL FIELD. An optional field allowing extra info to be added if necessary. No problem to leave blank." markdown editor="simplemde" html="true"></perch:if>
                                            <ul class="button-nav pill">
                                                <li>
                                                    <button class="bkg-green-light bkg-hover-tdc-red color-white color-hover-white medium">
                                                        <span class="icon-old-phone small"></span>
                                                        <a href="tel:+33685880591">Call Us</a>
                                                    </button>
                                                </li>
                                                <li>
                                                    <button class="bkg-blue-light bkg-hover-tdc-red color-white color-hover-white medium">
                                                        <span class="icon-credit-card small"></span>
                                                        <a href="../contact/booking.php">Book Online</a>
                                                    </button>
                                                </li>
                                            </ul>

Safari Source Code for the same section:

<ul class="button-nav pill">
                                                <li>
                                                    <button class="bkg-green-light bkg-hover-tdc-red color-white color-hover-white medium">
                                                        <span class="icon-old-phone small"></span>
                                                        <a href="tel:+33615553156">Call Us</a>
                                                    </button>
                                                </li>
                                                <li>
                                                    <button class="bkg-blue-light bkg-hover-tdc-red color-white color-hover-white medium">
                                                        <span class="icon-credit-card small"></span>
                                                        <a href="../contact/booking.html">Book Online</a>
                                                    </button>
                                                </li>
                                            </ul>

Any help gratefully received.

Many thanks

Diagnostics:

Health check

 Perch is out of date. You are running Perch 3.1.2 and the latest is 3.1.3. Update instructions
 PHP 5.6.30 is up to date
 MySQL 5.6.32-78.1 is up to date
 Image processing available
Summary information

Perch: 3.1.2, PHP: 5.6.30, MySQL: 5.6.32-78.1, with PDO
Server OS: Linux, cgi-fcgi
Installed apps: content (3.1.2), assets (3.1.2), categories (3.1.2), perch_forms (1.12)
App runtimes: <?php $apps_list = [ 'perch_forms' ];
PERCH_LOGINPATH: /perch
PERCH_PATH: /home1/silverpe/websites/tdc-website/perch
PERCH_CORE: /home1/silverpe/websites/tdc-website/perch/core
PERCH_RESFILEPATH: /home1/silverpe/websites/tdc-website/perch/resources
Image manipulation: GD Imagick
PHP limits: Max upload 64M, Max POST 64M, Memory: 256M, Total max file upload: 64M
F1: 3b606135b33e6a102526838f4152a807
Resource folder writeable: Yes
DOCUMENT_ROOT: /home1/silverpe/websites/tdc-website
HTTP_HOST: www.tdcski.com
REQUEST_URI: /perch/core/settings/diagnostics/
SCRIPT_NAME: /perch/core/settings/diagnostics/index.php