they subsequently clarified the rule (i.e. the "extra" place is given to the CL winner) but at the time I thought it was ambiguous??
After all, the previous time it happened, 2000, the 4th place Spanish team went to the UEFA cup to allow Real Madrid to defend the CL. I remember at the time that being the precedent that people were concerned about.
anyway, here's the relevant rule on the PL website for this season:
"In the event that a Premier League club win the UEFA Champions League and another win the UEFA Europa League and neither of these clubs finish in the top four of the Premier League, the club lying fourth in the table will drop into the UEFA Europa League group stage."