You will not be able to book a free companion on your free return booking all together. Our free returns are valid for the same number of paid guests that visited the first time, as companions and under 3's are free they are not included on a free return. Essential companion tickets need to be booked separately.
If you already have an Access Card/applied through Nimbus for your first visit and have been awarded the +1 essential companion requirement, you will be able to book your free essential companion ticket online here or collect one on the day from the Ticket Office with your Nimbus ID details.