The half-hour speech, touching on everything from the economy to global security and the values Canada shares with the United Kingdom, included a pitch for the prized trade agreement long sought by Harper's Conservative government.
"It remains our hope that we will soon achieve a comprehensive economic and trade agreement with the European Union, Canada's second-largest trading partner after the United States," Harper said.
"For Canada, and for Great Britain as a member of the EU, this will be a historic step — a monumental one, in fact: A joint Canada-EU study has shown that a commercial agreement of this type would increase two-way trade by twenty per cent.
"In this matter, as in global trade matters generally, prime minister, I should like to express my deep appreciation to you and to your government, for your robust advocacy on behalf of this agreement. It will be a great benefit to all of our citizens."
Canadian negotiators are under growing pressure to broker a deal with the Europeans before they turn their attention to free trade talks with the United States.
Among the issues believed to be on the negotiating table are financial services, Canadian beef exports, procurement limits for provinces and municipalities and drug patent protection.
However, Harper insisted this week that an "artificial timeline" will not loom over the talks, and that a deal will not be signed unless it is in Canada's best interests. The Prime Minister's Office has played down suggestions an agreement will be reached while Harper is in Europe ahead of the G8 summit in Northern Ireland.
The prime minister's pitch included talk of Canada's economic strength relative to much of the rest of the world. Harper argued, as he often has in the past, against protectionism and touted trade as the main driver of prosperity.
"Another value whose certainty has been repeatedly proven, though sadly sometimes more in the breach than the application, is that everyone gains in an open economy," Harper said.
"Our businesses grow when new markets are opened."
The prime minister also said tried-and-true measures are the way to deal with the problems confronting the global economy.
"What we need for the new challenges of a new world is not a new set of values," Harper said.
"It is the steadfast resolve to fully apply those time-honoured principles that we already know work. Certainly, that has been the Canadian approach to the economy which, I know, prime minister, is the top priority for both your government and mine."
Turning to global security, Harper called Israel the "only true western democracy" in the Middle East, and identified the Iranian and Syrian regimes as threats to peace and stability.
"Iran's leaders openly brag that they will eliminate Israel from the face of the earth," Harper said. "This is a profoundly malevolent regime that threatens us all, and whose first victims are the Iranian people themselves."
On Syria, where President Bashar al-Assad's regime is in the throes of a bloody civil war with rebel factions, Harper offered no solution to ending the two-year conflict.
"Herein lies a grotesque dilemma: decent people agree that Assad must go, that Syria's government must represent all its people, including its minorities," the prime minister said.
"Yet the extremist, sectarian nature of much of the opposition cannot be ignored or wished away. And Syria cannot be allowed to become another safe haven for the hydra-heads of terrorism.
"Such monsters already lurk far too close to home, as we have seen in the murder of Drummer Rigby ... and the foiled plot in Canada to sabotage a Via Rail express."
British soldier Lee Rigby was killed last month on a street in southeast London by a pair of attackers espousing militant Islam.
Harper is the first sitting Canadian prime minister to formally address the British parliament since the Second World War, when William Lyon Mackenzie King spoke in Westminster's Royal Gallery only weeks before D-Day.
After the speech, the Speaker of the House of Lords, Baroness Frances D'Souza, brought up Senate reform.
"It is of particular significance to me that both our parliaments have appointed upper chambers," she said.
"Today, the Canadian Senate and the House of Lords face difficult questions of reform. The future of both chambers is a issue that often preoccupies commentators and politicians on either side of the Atlantic. And I know that this is a matter of particular interest to you.
"But as we have discovered here recently, during debates on the draft House of Lords reform bill, there are no easy solutions. I shall watch developments in Canada with great interest ... who knows? Where one chamber goes, the other may follow."
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