David's link shows Jim Russell in a Lotus 11-Alta and Tony Brooks in a Lotus 9-Lea Francis. So are we talking about two different cars?
I don't think so. The reports in Autocar and Autosport magazines refer to Brooks in a Lotus-Connaught, with Russell not mentioned, while Motor Sport refers to Russell in a Lotus-Connaught, with Brooks not mentioned.
Also, the Motor Sport report doesn't state that Russell was in a Lotus Eleven Connaught. The only type number referred to in any of the reports was Chapman's Eleven.
Autocar (13 July 56) Silverstone F2 race preview
“ Brooks has been chosen by John Coombs to drive his Connaught…
Autocar (20 July 56) report
20 starters included eight Lotus Climax (3 of them 1100cc), a Lotus-Connaught driven by Tony Brooks, a Lotus-Maserati. Russell not mentioned at all. The only Lotus referred to by a type number was Chapman’s Eleven.
Autosport (13 July 56) preview
Entry list included Lotus-Connaught, Tony Brooks. Russell not listed.
Autosport (20 July 56) report
20 starters. 9 Lotuses including Brooks’ Lotus-Connaught, Naylor Lotus-Maserati.
Grid does not include Russell.
“Tony Brooks was soon to retire his Lotus-Connaught with brake trouble”
No type numbers given for any cars.
Motor Sport (August 56) report.
Field included 9 Lotuses, including Russell (Lotus Connaught).
“Russell had to retire the Lotus Connaught with negative brakes”
Brooks not mentioned. No type numbers given for any cars.
So it would seem to be the one car (of John Coombs), not necessarily an Eleven, & driven by either Brooks or Russell.