According to this BBC article from late last year the team had re-organised & were back to 9. Surely therefore with the departure of Flt Lt Stewart they are back to 8 not 7
The decision to reduce to seven is because the displays would look "odd" with eight - which I agree they do.
Obviously the Patrouille de France fly with eight planes as standard but their formations are designed with this in mind. Presumably too late to make this change now so seven is the easy answer.