Nicholas Bohm, via the ORG list, recommends an excellent article "Privacy in Public Places" by N.A. Moreham in the Cambridge Law Journal for November 2006 -  CLJ 606.
"ONE of the most difficult questions facing English courts as they
develop the common law right to privacy recognised by the House
of Lords in Campbell v. MGN Ltd.1 is whether and, if so, when a
person might have a reasonable expectation of privacy in a public
place. Should an individual have a cause of action if she is
photographed as she leaves her mother’s funeral or as he receives
medical attention after an accident? Or should there be an absolute
rule which says that there is no privacy in a public space? Recent
decisions in England and the European Court of Human Rights
(ECtHR) suggest that it is no longer an answer (if it ever was)
simply to say that the disclosure concerned something which took
place in public. A more difficult question therefore remains: if the
existence of a privacy interest does not depend on the nature of the
space in which claimants find themselves, how do we determine
whether a person does have a legitimate privacy interest...
This article looks at how the courts should answer this question
when the claimant is in a public place (i.e., places such as parks,
beaches, restaurants, bars and sports facilities to which members of
the public have access, either freely or on payment of a fee)...
The article rests on the premise that by
carefully examining dicta in existing case law and by identifying
underlying principles, one can begin to identify a coherent framework
for the protection of privacy in public places in English law."