SCHEMA:
CREATE TABLE table_25831483_1 (actor_actress VARCHAR, character VARCHAR, last_appearance VARCHAR, total VARCHAR)
USER:
Who was the actor/actress with a last appearance of 1 january 2010 and total is 20 and character is vanessa 'nessa' jenkins?

QUERY:
SELECT actor_actress FROM table_25831483_1 WHERE last_appearance = "1 January 2010" AND total = 20 AND character = "Vanessa 'Nessa' Jenkins"