David Cameron called for a step-change in trade links between Britain and Turkey today, setting out an ambition of doubling their value over the next five years.
Speaking to business leaders in Ankara, the Prime Minister said Turkey was vital for the UK's economy, security and diplomacy.
Seeking to strengthen relations between the two countries, he criticised those who oppose Turkey joining the European Union, saying they made him "angry".
And he said Turkey ought to be Britain's most important trade partner in Europe.
"Everyone's talking about the BRICs - the fast-growing emerging economies of Brazil, Russia, India and China," he said.
"Turkey is Europe's BRIC. And yet we export more to Ireland than we export to Brazil, Russia, India, China and Turkey all combined.
"No disrespect to our partners in Ireland, but we have to change that."
Speaking to Turkey's equivalent of the British chambers of commerce, he called for less protectionism and more Turkish investment in the UK.
"We're encouraging British business to be more ambitious in developing new markets - as Turkish business has done," he said.
"Vodafone, Tesco and HSBC are just three of the big British investments already in Turkey. I want to see many, many more.
"Today the value of our trade is over nine billion dollars a year. I want us to double this over the next five years.
"We cannot let the protectionists win. The truth is that trade is the biggest wealth creator we've ever known, and it's the biggest stimulus we can give our economies right now."
Mr Cameron's comments came as he took aim at those creating obstacles to Turkey joining the EU, including France and Germany. Many Tory right-wingers also oppose the idea of a Muslim country becoming a member of the bloc.
He said Turkey had a right to be a member, given its support for Nato, including in Afghanistan.
"I believe it is just wrong to say Turkey can guard the camp but not be allowed to sit inside the tent," he said.
"So I will remain your strongest possible advocate for EU membership and for greater influence at the top table of European diplomacy."
He likened Turkey's difficulties now to Britain's when former French president Charles de Gaulle sought to block the UK's entry to the EU.
"We know what it's like to be shut out of the club," he said.
Mr Cameron hailed Turkey's influence for good in the Middle East and said that the country could be "a great unifier" between the East and West.
Describing the Turkish state as "secular and democratic", he added: "This is all the more reason to make Turkey feel welcome in Europe."
Earlier, Mr Cameron paid tribute to the founder of modern secular Turkey, Mustafa Kemal Ataturk, who led the Turkish War of Independence.
After laying a wreath at Ataturk's mausoleum at Anitkabir, he wrote in the commemoration book: "I recall, first visiting Turkey 20 years ago, the emotion and power of the words Ataturk wrote for the war memorial for those who died at Gallipoli.
"I was struck at the time by the incredible warmth and generosity referring to the Mehmets and Johnnies and how the Turkish nation would now care for them both.
"I believe that today there is the greatest possible opportunity for a strong partnership between our two countries and I will work to help bring that about."
Mr Cameron's trip to Turkey is only his fifth bilateral overseas visit since becoming Prime Minister and is meant to underline his commitment to deepening relations with the country.
After talks with Turkish Prime Minister Recep Tayyip Erdogan, Mr Cameron will take his trade push on to India.
He will be backed up for the India leg by a 67-strong delegation of British ministers, business leaders and cultural representatives.
The Prime Minister, who flew out to Turkey yesterday, will be picked up from Ankara by a chartered aircraft transporting the group from London to India.
It includes six other ministers - Foreign Secretary William Hague, Chancellor George Osborne, Business Secretary Vince Cable, Culture Secretary Jeremy Hunt, Universities Minister David Willetts and Energy Minister Greg Barker.
Some of the UK's most senior chief executives and chairmen will also attend, including Richard Olver, of BAE Systems, and John Varley, of Barclays bank.
Other firms represented include KPMG, Rolls-Royce, Vodafone and JCB. The heads of the CBI and Institute of Directors will also be there.
Former Olympic athletes Dame Kelly Holmes and Sir Steve Redgrave, and Premier League chief executive Richard Scudamore will be among a sporting contingent.
Universities including Cambridge, Exeter and Imperial College London are also sending representatives.
Jo Johnson, Tory MP (Orpington) and brother of London Mayor Boris Johnson, will attend as chairman of the all-party Parliamentary Group on India.