Slow DELETE in MySQL with a subquery
Try removing the nesting levels, mysql can not delete from a table that's referenced as a child, instead there's a propriety trick like:

    DELETE t1.* 
    FROM regulatory T1
    JOIN regulatory T2 
        ON t1.group_ID=v_user_id  
       AND t2.group_ID=v_user_id 
       AND TRIM(t1.title)=TRIM(t2.title) 
       AND TRIM(t1.spare1='red.gif') 
       AND t1.docref=v_temp
       AND t1.DocumentID&gt;t2.DocumentID


Also, like @Mihal suggested try removing all function calls like trim from predicates, they are expensive.