'go to hyde park and demand the truth'?

I couldn't read the rest of the banner but I assumed it was probably a religious group - Hyde Park is known as a place of religious and political oratory on Sundays.

I may be reading too much into it, but I felt there was a very low key religious message in the film - something that was quite common in films of that era.

Eg, the film takes place on Sunday, the 'religious' day of the week. None of the characters is a churchgoer, except the fence, who is a hypocrite who comes to a sticky end on the way home from church; and the only other religious characters are the Salvation Army band, who seem to be a cacophonous nuisance (one of the market traders shouts at them to shut up) and the group with the banner, who instead of loving their neighbours, march off to Hyde Park instead.

There are also several explicitly Jewish characters in the film, which was somewhat unusual for the time. Hyams (the Jewish boxing promoter) redeems himself to a certain extent by giving money to the vicar for the church club, despite the money being 'tainted'; showing that good can come sometimes still come out of evil.

The principle character is given a choice between good, represented by her husband and family life, which although a bit dull, is shown as the 'right' way; or evil, represented by Tommy Swann, who initially appears exciting but in fact he cares nothing for her and betrays her.