Treasure island tax

Cameron has made tackling tax avoidance - which campaigners say costs about $3 trillion a year - one of the key parts of the formal agenda at the summit.

He has turned up the pressure to clamp down on secretive money flows by pressing Britain's overseas tax havens into a transparency deal and announcing new disclosure rules for British firms.

"It is important we are getting our house in order," Cameron said on Saturday after representatives of overseas tax havens linked to Britain agreed to sign up to an international transparency protocol.

Aid campaigners said Britain's action will count for little if the rest of the G8 does not follow suit.

G8 leaders will probably shy away from adopting a measure aimed at curbing tax avoidance by highlighting when companies channel profits into tax havens, and will include a watered-down alternative, according to the draft communique.

Tackling corporate tax avoidance has become a political goal internationally following public anger about revelations over the past year that companies like Apple and Google had used structures US and European politicians said were contrived to minimise the amount of taxes paid.

But the draft summit text suggested there will be no agreement on a rule that would force companies to publish their profits, revenues and tax payments on a country-by-country basis.

Global tax evasion could be costing more than $3 trillion a year, according to researchers from Tax Justice Network while as much as $32 trillion could be hidden by individuals in tax havens.