What time period is in the BFG?

The time period in which The BFG is set is unknown. There is, however, one hint in the text, and that is that Sophie has sampled a few different carbonated beverages.... Coke and Pepsi. Coke has been available since 1886, Pepsi since 1898. There is also mention of British helicopters. Thus, we can infer the story takes place during the 20th Century.