As summary, some limits from case law:
Parliamentary expense declarations were not considered included in the privilege.
The privilege also doesn't cover parliamentary publications per se although a related (1840) statue does.
Declarations to the press by MPs also not covered. The way of referring to the previous floor statements outside of Parliament has affected the outcome of some (defamation) lawsuits. A qualified privilege seems to exist for such declarations, i.e. inclusion by reference might be difficult to prove in court as malicious, especially in a body of similar political declarations, but explicit repetition/reaffirmation of statements or excerpts may open the door for successful defamation suits.
An interesting case that was deemed outside the privilege in a (2010) court case was the declaration of parliamentary expenses:
The Chaytor case illustrates this well. The issue was whether matters concerning claims by a number of parliamentarians for parliamentary expenses could form the subject of
criminal prosecutions. Prosecutions were brought by the independent prosecuting
authority, the Crown Prosecution Service. The defendant parliamentarians argued
that such expenses claims were subject to parliamentary privilege and thus outwith
the court’s jurisdiction. Having set out the development of the relationship between
the courts and Parliament concerning privilege, and that it was for the courts to determine
whether something fell within the scope of privilege, the Supreme Court identified
the key issue. Lord Phillips of Worth Matravers PSC explained that the question
rested on whether scrutinising the expenses claims in criminal proceedings would
have an adverse impact on the core or essential business of Parliament and
whether it would inhibit debate or freedom of speech. He concluded that such scrutiny
would not “inhibit any of the varied activities in which Members of Parliament
indulge that bear in one way or another on their parliamentary duties. The only
thing that it would inhibit would be the making of dishonest claims” (para. 48).
Also noteworthy perhaps, the records of the Parliament, such as the Hansard are not covered by the privilege itself, but by a mirror statutory protection dating to 1840.
As the 1999 Joint Committee noted, “parliamentary privilege does not cloak
parliamentary publications with any form of protection”. This was decided in 1839 in the
case of Stockdale v. Hansard, in which the court held that parliamentary privilege did not
attach to the publishers of reports ordered to be printed by the House of Commons. The
Parliamentary Papers Act 1840, passed in response to this decision, established that no
action could be brought in court arising from the publication of the Official Report or
other documents ordered to be published by either House. It also provided protection for
“any extract or abstract” from such documents made by others, provided that it was
published “bonâ fide and without malice” (section 3). Such protection for publications by
order of either House is a matter of statute law, not privilege.
Regarding statements to the press by MPs, the situation is somewhat complicated:
The decision of the Judicial Committee of the Privy Council, which at that time was
the highest judicial authority for New Zealand, in Jennings v. Buchanan has caused us
some concern. In that judgment, delivered by the late Lord Bingham of Cornhill, it was
decided that Mr Jennings, a New Zealand MP, could be sued for defamation because he
had told a newspaper that he “did not resile” from the remarks he made in the New
Zealand House of Representatives about a New Zealand Wool Board official identifiable as
Mr Buchanan. Jennings v. Buchanan was a New Zealand case, and is not binding in the
British courts, though it would be highly persuasive. The Judicial Committee ruled that—
“A statement made out of Parliament may enjoy qualified privilege but will not enjoy
absolute privilege, even if reference is made to the earlier privileged statement. A
degree of circumspection is accordingly called for when a Member of Parliament is moved or pressed to repeat out of Parliament a potentially defamatory statement
previously made in Parliament”.
The Clerk of the New Zealand House of Representatives told us that the New Zealand
House of Representatives Privileges Committee had recommended legislation to deal with
the effective repetition problem from Jennings v. Buchanan, because it potentially inhibited
public discussion of what went on in Parliament, but that nothing had happened. Dr
Rosemary Laing, the Clerk of the Australian Senate, told us that “we take great care to warn
our Members about the possibility of a Jennings v. Buchanan-type action and urge them to
be careful about what they say outside of the proceedings in Parliament”.
This seems to be a weaker explicit protection than that enjoyed by US Congresspersons following the Westfall Act. But then there don't seem to have been a lot of UK or even Commonwealth cases triggering a need for stronger statutory protections for MP statements to the press. Actually in more recent UK case the plaintiff was unsuccessful.
In a recent United Kingdom case, Mr Justice Tugendhat struck out claims for slander
and libel brought against a witness to a select committee, Lord Triesman, who had
subsequently given evidence to a Football Association inquiry into allegations he had made
at the select committee hearing concerning the reasons for the failure of England’s bid to
host the World Cup in 2022. The plaintiff alleged that Lord Triesman had adopted by
reference and/or confirmed and/or repeated his statements made to the select committee.
This case demonstrates that the principle stated in Jennings v. Buchanan is far from
universal—each case is decided on very specific facts. The transcripts of the FA’s inquiry
showed that Lord Triesman had been careful not to go beyond what he had previously said
to the select committee: for example, “my evidence in respect of this issue is set out in the
transcript of the statement that I made to the Culture, Media and Sport Committee”.
Moreover, the judge ultimately ruled that the occasion (Lord Triesman’s evidence to the
FA’s inquiry) was itself one of qualified privilege, and that there was no case in malice that
could be left to a jury at trial.
The 2013-2014 Joint Committee on Parliamentary Privilege concluded (contra to the UK Government's opinion actually) that
In practice, this would mean that a Member who, for instance, published on his
website links to his contributions to debates, whether in the online version of Hansard or
the webcast of the sitting, would enjoy absolute privilege—while the specific link might be
to the Member’s personal speech, that speech would be part of a file in which the entire
day’s sitting or webcast (both issued under the authority of the House) was contained. If,
on the other hand, the Member reproduced the verbatim text of a speech (that is, an extract
from Hansard), the protection would be qualified, so any claimant would have to prove
malice in order to bring a successful suit. In normal circumstances (for instance, a
collection, whether printed or online, of the Member’s speeches on a variety of subjects), it
would be very unlikely that malice could be proved.
On the other hand, we acknowledge the risk that, just as conferring absolute privilege
upon reports of proceedings could encourage the media to channel defamatory or other
unlawful content through Members, thereby opening the door to unlimited publication, so
extending absolute privilege to the repetition by Members outside Parliament of statements
made by them in the course of proceedings might create a temptation for Members to
make reckless or defamatory statements in the course of debate, with a view to repeating
them outside. This could bring parliamentary proceedings themselves into disrepute.
So while we share the concern of our colleagues in New Zealand and Australian
legislatures at the potentially chilling effect of Lord Bingham’s judgment in Jennings v.
Buchanan, we do not under-estimate the complexity of legislating to extend Members’
absolute privilege of freedom of speech beyond actual proceedings in Parliament. Every
case will be unique, and cases where Members simply refer neutrally to speeches made in
Parliament may shade into others where they “have nothing to add”, “do not resile from”
or “re-affirm” those speeches. We doubt that legislation to codify these imperceptible
differences of emphasis is either feasible or desirable.