I came across this ad in a March 10, 1928 Women’s Life, which is a British magazine. I’d never heard of Virol-and-Milk before, so I decided to do some research. From the scant information I could find, I determined that Virol was a malt extract. In Virol-and-Milk, the extract was mixed with Devonshire full cream powdered milk and sold in tins. Consumers mixed the powder with hot (but not boiling) water.
Virol was sold by itself, and during WWII, British schoolchildren had to have a weekly dose in order to make sure they got the proper ration of vitamins. http://timewitnesses.org/english/food/Rations.html
There was also a product called Virolax which was (you guessed it), a laxative. I couldn’t find the ingredients for Virolax, but ads claimed it was "An elegant laxative Virolax for children and adults."