A protest against the Temperance movement in 1920. The advert is saying that the only real effect of an alcohol ban, as was seen in the US, would be to prevent the working class from accessing booze – those with money would always be able to pay their hands on it. I agree that “a sober working class” was, no doubt, desirable by those in charge.
And here’s a nice little picture of some members of the labour movement having fun – trade union delegates taking a break from the 1917 congress for a splash about on Blackpool beach. How great it would be if politicians did this at their party conferences now.