David Cameron has appealed to Stephen Harper, the Canadian Prime Minister, not to scupper an agreement at next week’s G8 summit on plans for a global crackdown on secret companies used for money laundering, tax evasion and terrorist activity.

But after talks in Downing Street last night it was doubtful whether Canada would back Mr Cameron’s “full disclosure” plan for the eight leading economies to create registers of who controls and owns every company based in their country. The “beneficial ownership” registers are seen as a vital component in a drive against global tax evasion, which will top the agenda when the G8 leaders meet in Northern Ireland on Monday and Tuesday.

In a statement after the talks, Downing Street said Mr Cameron and Mr Harper agreed that the G8 “should make progress on transparency”. However, the Canadian government still has concerns about a register being open to the public because of rules on taxpayer confidentiality and because under its federal system states play a role in tax decisions.

Download the new Independent Premium app Sharing the full story, not just the headlines

The US and Russia also have doubts about public registers. Mr Cameron may have to settle for a Plan B, under which the G8 nations would set up private registers that could be accessed only by tax and law enforcement authorities. It is not certain Canada would agree to that. Aid agencies say private registers would be second best because it would be harder for the world’s poorest countries to track individuals and businesses avoiding tax in their nations who hide behind anonymous “shell companies.”

Mr Cameron will make a similar plea to support public disclosure to Vladimir Putin, the Russian President, in talks at No 10 on Sunday, and to President Barack Obama before the summit gets under way on Monday.

Bermuda suggested it might sign up to a global tax information sharing scheme when the 10 British overseas territories and crown dependencies seen as tax havens meet Mr Cameron for talks in London tomorrow.

Craig Cannonier, Bermuda’s Prime Minister, appeared to contradict his earlier remarks by saying his country was “strongly committed” to joining the multilateral convention on tax.

“Bermuda is a well-regulated jurisdiction and has always been at the forefront of international efforts to fight tax evasion and aggressive tax avoidance,” he said. British officials hope all 10 tax havens will now sign up, giving Mr Cameron’s drive against tax avoidance a pre-summit boost.

Today Mr Cameron will announce that the Government will mark its chairmanship of the G8 club by putting £1m into a “prize fund” for a global challenge to identify and solve the biggest problem of our time. A Downing Street source said: “We want people to think big; what does the world need and how can we achieve that? We are looking for the next penicillin, aeroplane or World Wide Web. Can we grow limbs or create universal low carbon travel? Something that is going to really revolutionise what we do and how we live our lives – sending us sprinting ahead in the global race.”

Mr Cameron will tell a G8 Innovation Conference in London: “We’ve all got to open up our economies to innovation; we’ve got to nurture new ideas [and] attract the best and the brightest. A global race is under way and it is waiting for absolutely no one.”

Three people were arrested for trespass during a protest against Canada’s extraction of oil from its tar sands as Mr Harper addressed both Houses of Parliament.