When Lily Collins - the star of the American TV show Emily in Paris - announced she’d had a baby by surrogacy, a debate played out in her comments about the pros and cons of starting a family this way. Some of the criticism alleged that surrogacy is the preserve of the rich. In many countries commercial surrogacy – where the intended parents have a contract and pay a fee to the surrogate – is legal, including the US, Mexico and Colombia. In the UK, however, only altruistic surrogacy is legal. Katarina Trimmings from the University of Aberdeen explains what this means and how the UK law on surrogacy works.