With the Leveson inquiry in mind, let me explore the implications of the Duchess of Cambridge pictures episode (see here and here).

France has a strict privacy law that is supposed to protect people from the unwanted attentions of the paparazzi. But it appears to make little difference to the country's intrusive celebrity magazines because they accept they will be fined.

The fines are relatively small – usually less than €30,000 – so publishers view the problem of whether or not to publish in commercial terms.

They make a cynical calculation based on the improved revenue through extra sales set against the amount they will be fined for breaking the law.

So let's suppose that some kind of privacy legislation were to be introduced in Britain. Surely publishers and editors would do as the French do.

Of course, fines could be higher than in France - and perhaps higher still for repeated offences - but there would have to be a sensible upper limit.

Anyway, a new privacy law isn't going to be enacted here. So, in practical terms, privacy intrusions within Britain will be dealt with, as now, through a system of press regulation or, in the courts, through actions based on article 8 of the European convention of human rights.

So let's imagine that Leveson recommends a form of regulation that allows for newspapers and magazines to be fined for breaches of a code of ethics (this is likely given the industry's acceptance of enhanced penalties).

As with a privacy law, a similar outcome is quite possible. Editors may well risk fines in order to benefit from additional sales. They would also, as now, try to argue public interest justifications.

One new form of public interest defence has become crucial (as The Sun showed when publishing the Prince Harry photo). If pictures are published on websites across the world, and can therefore be deemed to be "in the public domain", then why not allow them to be carried on British news websites?

As Lord Justice Leveson recognises, it is impossible to regulate what happens outside Britain's jurisdiction. Print imported into Britain can be constrained; online material cannot.

So let's take another flight of fancy by asking what might happen should the topless Kate pictures go viral, and therefore global. Say they reached similar levels of online publication to the Harry pictures, would Rupert Murdoch allow The Sun to publish by arguing - as he did with the Prince Harry picture - that it's all a matter of press freedom?

I doubt that he would contemplate publishing these particular pictures, not least because of a possible negative public reaction at a time when the paper is on the back foot over its Hillsborough coverage.

Then again, note that the Palace huffed and puffed about The Sun's use of the Prince Harry picture, and then sat on its hands. It did not make a formal complaint to the Press Complaints Commission, implying that it acknowledged the strength of the paper's argument.

Deciding where to draw lines in such matters remains problematic.