Thanks for looking into this Ray.
Turning on error reporting reveals
' Fatal error: Call to a member function Prepare() on null in /home/sites/XXXXXXXX.co.uk/public_html/webassist/mysqli/queryobj.php on line 476 '
This suggested to me that there was an issue with email logging and when looking into the database I found an empty table (set to latin_swedish_ci collation!).
Deleting this table did not change the error status and the table was not recreated hence my feeling that things must be locking up here and not allowing the page to load.
I have only run the Universal Email routine an have made no other edits.
Many thanks in advance.