Used to start all 4 with a mass rapid start from OUTSIDE the aircraft ! At Scampton in the mid 60s.
on one memorable occasion the engines were started from outside but the key to the entrance door - which I think was secured round the nav radars neck ? had been temporarily lost / forgotten - so the aircraft was throbbing away with the crew stuck outside!
can’t remember for how long the engines were running unattended but I think it was for quite a long time!
this method was stopped shortly afterwards!