Britain is drawing up plans to ensure that any EU action against Russia over Ukraine will exempt the City of London, according to a secret government document photographed in Downing Street.

As David Cameron said Britain and its EU partners would put pressure on Moscow after it assumed control of Crimea, a government document drawn up for a meeting of senior ministers said that "London's financial centre" should not be closed to Russians. It did say that visa restrictions and travel bans could be imposed on Russian officials.

The picture of the document was taken by the freelance photographer Steve Back, who specialises in spotting secret documents carried openly by officials entering Downing Street. The document was in the hands of an unnamed official attending a meeting of the national security council (NSC) called by the prime minister to discuss the Ukrainian crisis.

The document said Britain should:

• "Not support, for now, trade sanctions … or close London's financial centre to Russians."

• Be prepared to join other EU countries in imposing "visa restrictions/travel bans" on Russian officials.

• "Discourage any discussions (eg at Nato) of contingency military preparations."

• Embark on "contingency EU work on providing Ukraine with alternative gas [supplies] if Russia cuts them off".

• Specific threats to Russia should be "contingent and used for private messaging" while public statements should "stick to generic" point.

• Draw up a technical assistance package for Ukraine "ideally jointly with Germany".

• Pursue the "deployment of OSCE and/or UN (but not EU) monitors in Crimea and eastern Ukraine".

• Push the "UN secretary general Ban to take the lead in calling and creating a forum for engaging Russia on Ukraine".

• Accept an emergency summit of EU leaders to discuss Ukraine. This will now be held in Brussels on Thursday.

Government officials said that no decisions were taken at the meeting of the NSC, but they confirmed that the call in the document for London's financial centre to kept open to Russians reflected the government's thinking that it wanted to target action against Moscow and not damage British interests.

The prime minister told the NSC that the government may be prepared to support EU sanctions that would be targeted at Russian businesspeople seeking to visit the EU. There could also be a "dialling down" of economic co-operation.

But nothing would be agreed that could harm the British economy. One source said: "You want to make sure that the costs fall more on Russia than other people."

Downing Street trod a careful line during the day as it made clear that action would need to be taken on the diplomatic and economic – though not the military – front to punish Russia. But it does not want to give Russia an excuse to refuse to embark on dialogue with Ukraine and the EU.

The prime minister highlighted this approach when he said after the NSC: "What we want to see is a de-escalation rather than a continuation down the path that the Russian government has taken, violating the sovereignty and territorial integrity of another country. So we shall have to bring to bear diplomatic, political, economic and other pressures in order to make this point. That is the very clear message the whole world needs to send to the Russian government."

Downing Street had earlier ruled out a military response in the wake of the Russian takeover of Crimea. The prime minister's spokesman said: "The only avenue that is being pursued is a peaceful and diplomatic one. Our other G7 partners have been very clear about that as well." The prime minister agreed in separate phone calls with François Hollande and Angela Merkel that the international community should speak with one voice on Ukraine as it tells Russia that its actions are "completely unacceptable".

A No 10 spokesperson said: "In both calls, the leaders agreed that the international community should speak with one voice and send a clear message to Russia that its actions in Ukraine were completely unacceptable. They agreed they must continue to work very closely together in response to events in Ukraine including in preparation for the special European Council which has been called on Thursday. It would be important to be clear about the costs and consequences for the Russian government of continuing to violate Ukraine's sovereignty; and of supporting the people and government of Ukraine in support of their efforts to build an inclusive Government and tackle economic challenges.

"They agreed there could be an important role for the United Nations, and potentially other international organisations, in facilitating the dialogue between the Russian and Ukrainian authorities which is central to the shared objective of de-escalating tensions in the region."

Former US presidential candidate Senator John McCain said he was "disappointed" by the UK's position and said European countries were "ignoring the lessons of history".

Asked if it was right to avoid such sanctions, he said: "Of course not. I am not astonished, to be very frank with you. Disappointed, but not astonished."