Most undertakers have a fleet of hea***s.. so a spare one can usually be made availbale.
Went to a funeral 5 years ago in a mid 1970s Daimler hea*** with the 4.2 Jag engine with SU Carbs... smelt like the mix was over-rich and it could burst into flames any minute.. (did not but nasty).. Brighton of course: lots of OAPs retire there to die..
Wouldn't it have been more appropriate for her cars to be hybrids? The short journeys could then be done on the electric motor (at least started off in that mode). Not sure what the public (or HM herself) would think of using a Prius or RX450h...