The Commons leader is one of five cabinet ministers understood to be hoping to amend Theresa May's plan.
No arrests have been made in connection with the shooting in north London.
Once one of the BBC's best known personalities, he introduced the first TV news bulletin in 1954.
Five major bridges were closed to traffic by protesters demanding greater action on global warming.
The "train emerged the victor" in the smash which left a silver Mercedes badly damaged, police say.