I have verified through the GRO indices that the Mark Edward Francis BENNETT who died Q4 2008 was born in 1960, so the probate entry is almost certainly the correct person.
I don't believe it follows that Peter BENNETT has died - Algernon is descended from the 2nd son of the 1st Bt, whilst Peter is the 3rd son of the 1st Bt. Nonetheless, there is evidence that he has died.
Peter BENNETT - according to Electoral Roll records, he was resident at an address in West Byfleet KT14 with Monique Christine Bennett until 2016. She continues in residence to the current day, suggesting he died in 2016. Other residents include Melissa Lucie BENNETT & Tiffany Claire BENNETT. Further work indicates they were daughters of Peter & Monique, born 1971 and 1973 respectively. Neither dau listed in DB 2003
There are a lot of Peter BENNETT deaths out there, but careful checking of GRO indices suggests this death:
BENNETT, PETER YoB 1938
GRO Reference: DOR Q3/2016 in SURREY (759-1D) Entry Number 514125149
This
might be the Peter BENNETT who died 17 July 2016 listed on the probate indices