Mal Fletcher comments

And what about the possibility of human-robot marriages? This may sound far-fetched, but wi-fi was sci-fi not long ago. Academics at Wellington University in New Zealand are predicting that robotic prostitutes will take over from their human counterparts within the next 30 years.

Sony is now studying Robot Anthropology, in order to understand or project how robots will interact with human beings in the next decade or so. Meanwhile, we are increasingly anthropomorphising machines and sophisticated, humanoid sex toys are already finding their way onto the market.

If, as many technologists expect, we will increasingly relate to robots as if they were human, why would human-machine marriages not become a desirable objective for some people? Wouldn't denying the possibility interfere with their right to self-expression?

These are not pie-in-the-sky questions for future generations. They are scenarios already made plausible by rapidly developing technologies. We must ask the question: what happens to marriage in ten years if we further deconstruct it now?

Instead of cynically using the marriage unit for political purposes, as a way of projecting his own liberal views, Mr Cameron should pause to reflect on what constitutes a true debate - and what makes the core of a stable family.

He should think carefully what traditional marriage means to this country, psychologically, sociologically and economically. The fact that many marriages have failed is no reason for deconstructing the institution itself.

If the Prime Minister wants a debate on the shape and health of family and marriage, as he says he does, then he should open his mind and his government to an honest, forthright and prolonged discussion.