Downing Street said that Cameron would make a "principled case" against Juncker at the summit.
Speaking in Berlin, the former Luxembourg prime minister appeared to criticise Cameron: "I am not designated commission president yet. If common sense prevails this will happen at the end of the week – but it seems common sense is very unequally distributed so one will have to wait."
Juncker spoke out as Downing Street confirmed that Cameron would force a vote on his nomination at the EU summit on Friday to highlight Britain's opposition.
Downing Street believes the European council (the EU's 28 leaders) are breaking with the precedent that senior EU appointments are made by consensus; this view suggests the council has fallen victim to what No 10 calls a backroom power grab by the European parliament.
Juncker is the candidate of the EPP, the main centre-right group in the European parliament, which emerged with the largest number of MEPs in last month's European elections. Under the Lisbon treaty EU leaders nominate the commission president, taking account of the elections. The European parliament then has to approve the candidate.
Cameron's spokesman said: "The prime minister's focus is [on] making the case, the principled case. He believes there should be a vote if the European council chooses to move away from a consensus-led approach. Of course we will look at all the ways we can best make our arguments. But our approach is very much one of seeking a vote and that is what we have been consistently saying."
Downing Street highlighted the prime minister's hardball tactics over the EU when it confirmed that Britain would block Albania from joining the EUunless tougher restrictions were introduced on its citizens travelling to existing EU member states. EU foreign ministers meeting in Luxembourg agreed to give Albania candidate status, allowing the former Communist state to take a further step towards formal membership negotiations. The decision will have to be approved by EU leaders at their summit.
Downing Street said Britain would be prepared to veto Albania's eventual membership unless Cameron's plans to restrict freedom of movement for citizens of new member states were agreed. In an FT article last year the prime minister said that restrictions could remain in place on a new member states until "a certain income or economic output per head".
The prime minister's proposal is a significant hardening of the current system of "transitional controls" which allow existing member states to impose restrictions for seven years after a country joins the EU. Britain imposed no controls on the 10 countries, including Poland which joined the EU in 2004.
The prime minister's spokesman said: "We will block any possible future accession from any country if the types of new and tougher transitional controls the prime minister has spoken about are not in place. That will apply to any and all future accessions, including the Albanian one.
"Negotiations have taken, in some countries decades, so this is a decision that's a very considerable period away. But the prime minister is very clear: for any and all accessions, new transitional rules must apply. Accessions require unanimity and the prime minister won't agree unless there are tougher rules."
The No 10 warnings came as Matteo Renzi, Italy's prime minister, likened the European commission to an "old boring aunt". In a speech to the Italian parliament he described the "shopping list" of fiscal recommendations from the commission as "an old boring aunt telling us what to do".
Renzi, a centre-left leader, endorses Juncker in the belief that he could ease the commission's austerity measures.
guardian.co.uk © Guardian News and Media Limited 2010