The Exposed campaign against corruption has issued an open letter to world government, business and church leaders telling them to "stop patronising the poor".

The letter has been issued in the run-up to Exposed's Week of Action from 14 to 20th October when people around the world will hold vigils against corruption and be asked to sign a petition that will be presented to the G20 summit in Brisbane next year.

In the letter, the Exposed campaign urges government, financial institutions and church leaders to act decisively and quickly on corruption.

They warn that tax evasion, bribery, secret business deals, and corrupt fiscal and government practices are "unjust and damaging to economies".

The campaigners welcome efforts to ensure multinational corporations pay their fair share of tax in the countries where they earn their profits, noting that an estimated $1trillion goes missing from the global economy each year in bribes and another $21trillion is hidden in tax havens.

However, they add that corruption is one of the main causes of poverty.

"Exposed – which is a global call to action against corruption in all its forms – wants to remind the leaders of the world, international corporations and the church, that in all of this we should not forget those who are most affected by greed and abuse of public influence – the poorest people of our world," they say.

"We should be ashamed that in 2013 there are still so many people blighted by dire poverty. In a world where there are more than enough resources to go around, if only they were more fairly shared, it is time for action on one of the main causes of poverty – corruption."

The campaigners go on to remind global leaders of the need to include poorer nations in decision making.

"Consensus on financial transparency is vital, as is international collaboration to ensure that corruption in all its forms is exposed and dealt with. But the poor can't wait for years of deliberation and diplomacy," they say.

"This is not just about 'rich countries' making changes to improve their tax income or making improvements which may, eventually, benefit 'poor countries'. It is about justice. The time has come to stop patronising the poor."

During the Week of Action, a vigil against corruption will be taking place on the steps of St Paul's Cathedral in London at 6pm on Monday October 14. Other vigils being planned for the week include one outside the White House in Washington DC.