The First World War was the event that served to introduce large numbers of British women to their first pair of trousers, says Ms Harden.
Women were literally, as well as figuratively, wearing the trousers, as they temporarily took up the jobs their soldier fathers, brothers and husbands had vacated.
In the inter-war years, trousers for women became acceptable for the upper classes, and ranges of leisure and sports wear were not complete without baggy, floor brushing, light fabric ladies' trews.
By the 30s, film stars like Katharine Hepburn and Lauren Bacall had put the Hollywood stamp of glamour onto women's trousers, which during the 20s were only worn in the country or for sport.
"The Hollywood touch was very important at the time in terms of whether a look became fashionable or not," says Ms Harden.
And then the Second World War made women and utility trousers almost inseparable. Land girls and munitions workers couldn't really do their jobs in skirts - and besides, there just wasn't enough material available to waste on the non-functional.