Button not refreshing page

Because onsubmit event not working with “input” tag.
You can see more details in https://www.w3schools.com/jsref/event_onsubmit.asp

Supported HTML tags: form, keygen

Replace code to

<form method="post"  onSubmit="window.location.reload()">
   <input type="submit" name="switchlon" id="switchlon" value="Switch to London" /><br/>
</form>

or

<form method="post" >
   <input type="submit" name="switchlon" id="switchlon"  onClick="window.location.reload()" value="Switch to London" /><br/>
</form>