Start with the first error mentioned by the validator.
Fix that one.
revalidate.
Repeat as needed.
It's important to start with the first listed error as that may cause the validator to flag a cascade of errors based on that one.
As shipped, the templates start with valid XHTML 1.0-Transitional so it's likely that changes to the pages have been the source of the errata.
Here's a few hints:
1) the <meta http-equiv="PRAGMA" content="NO-CACHE">
<meta http-equiv="REFRESH" content="300">
is in the <body> section and needs to be in the <head> section. For XHTML compliance, it also has to have closed tags like <meta http-equiv="PRAGMA" content="NO-CACHE"/>
<meta http-equiv="REFRESH" content="300"/>
2) the Newton Poppleford, Devon, United Kingdom</br>
should be Newton Poppleford, Devon, United Kingdom<br/>
XHTML has self-closing codes for <meta .../>, <br/>, <img .../>, <hr/>
Hope this helps...
Best regards,
Ken