I have resolved this one myself finally.
I made the following change to the search/tabs.html.tmpl file
[% IF user.in_group("admin") %]
[% tabs = [ { name => 'specific', label => "Simple Search",
link => "query.cgi?format=specific" },
{ name => 'advanced', label => "Advanced Search",
link => "query.cgi?format=advanced" } ] %]
[% ELSE %]
[% tabs = [ { name => 'specific', label => "Simple Search",
link => "query.cgi?format=specific" } ] %]
[% END %]