As is often the case, shortly after posting my question above I worked out what I needed to do. Firstly Entity Permissions needed to be setup to allow Read of activitymimeattachment's. I then used the following FetchXML and Liquid to retrieve and display the information I wanted:
{% fetchxml attachment_query %}
<fetch >
<entity name="activitymimeattachment" >
<attribute name="attachmentnumber" />
<attribute name="filename" />
<attribute name="filesize" />
<attribute name="attachmentid" />
<filter>
<condition attribute="activityid" operator="eq" value="{{ emailResult['activityid'] }}" />
</filter>
</entity>
</fetch>
{% endfetchxml %}
<div class="email">
<ul class="attachments">
{% for attachment in attachment_query.results.entities %}
<li><a href="/_entity/activitymimeattachment/{{ attachment['attachmentid'].id | h }}">{{ attachment['filename'] }}</a></li>
{% endfor %}
</ul>
<div class="sendon"><b>Date Sent:</b> {{ emailResult['senton'] }}</div>
<div class="subject"><b>Subject:</b> {{ emailResult['subject'] }}</div>
<div class="body">{{ emailResult['description'] }}</div>
</div>
One interesting thing to note here is that clicking on the attachment link downloads the file as you would expect which is exactly what I wanted.
Thanks
