Worked it out
function sherwood_get_posts( $category_name )
{
// set the criteria
$args = array(
'numberposts' => -1,
'post_type' => 'custom_type',
'tax_query' => array(
array(
'taxonomy' => 'custom_cat',
'field' => 'slug',
'terms' => array($category_name))
)
);
// return the object array of the posts.
return get_posts( $args );
}
?>