The same year that 'THE SECRET SKETCHBOOK' was published (1969) saw the release of 'THE SECOND COMING OF TOULOUSE LAUTREC', Searle's homage to the great French Impressionist of short stature with a penchant for hanging out in brothels.
The Hamburg sketches are signed & dated 1967 while the Lautrec drawings are dated 1969. It seems Searle's experience drawing the strippers of Hamburg directly informed the later 'imaginary' works, perhaps even inspiring the project. Searle could certainly now identify with Lautrec (to a degree) as an artist amongst 'les femmes de nuit'.
The women in the Lautrec project are drawn in the same loose manner as the 'Secret Sketchbook' & have the same realistic, 'womanly' proportions, un-glamorised female figures.
'Inscribed on the title page in black ink “For / Wendy / with love & / Happy Birthday wishes / - this bit of / backstreet reporting / by two of your / chums! / ? and Ronnie [underlined].” Beside the inscription Searle has drawn full page illustration of a cigarette smoking Fille de Hambourg in heels and stockings which he has dated underneath 1st May 1969. The recipient is actress, choreographer, stage and film director Wendy Toye with whom Searle collaborated on several projects.' -Lucius Books
Here's the real sketchbook at the Searle archive in Hanover, Germany.