Afghanistan’s president, Ashraf Ghani, has said he has no issue with David Cameron calling his country fantastically corrupt ahead of Thursday’s Commonwealth anti-corruption conference in London.

Ghani said: “He was describing the legacy of the past. Many actors, many factors combined to produce one of the most corrupt countries on earth. But that is not the desire of our people and I have been elected on a mandate to make transparency, accountability and the rule of law the imperative.

“The first part of addressing the problem begins with acknowledgement and we are partners in an effort to overcome this cancer. What distinguishes my government is our clarity about what we’ve inherited, our determination to address it, our willingness to form the right partnerships.”

He said the west had a duty to help as “the most significant driver of corruption is the narcotic cartel”, driving both terrorism, extremism and corruption.

Under Ghani’s leadership, Afghanistan has fallen in the index of corruption compiled by campaign group Transparency International to 166th – better only than North Korea and Somalia. Appearing on BBC Radio 4’s Today programme, Ghani said the way the index was calculated did not reflect underlying work that was yet to bear fruit – pointing out that Britain had taken decades to tackle the issue in the past.

“England was the first to invent grand corruption in the 18th century. It took decades to overcome it. We don’t ask for decades but this is a process of change,” he said.

Asked about the EU envoy to Afghanistan’s claims that the biggest problem in the country was impunity, which was a responsibility of his government to address, he said: “Absolutely, but the same European envoy I hosted in the presidential palace, where I gave the keynote speech, I announced the creation of the counter-corruption centre doubling its force. We have a special crimes taskforce that the UK has generally supported in the past but had been marginalised because when they started working in the previous era and arrested somebody in the palace their entire operation was discontinued.

“This is exactly what we are addressing and now we have a reformist attorney general, a reformist supreme court justice, we have changed over 600 judges in this period, now we are attempting a wholesale transformation of the prosecutorial culture, and then the police. But you have to have a rule of law approach and not just base it on any allegation, because the corrupt engage in the most intense propaganda when they are prosecuted and accused.

“I asked in that meeting that an ombudsman office be created and that all the donors agree as to what should be the criteria and who should be the person, so they can investigate any allegations against the palace, against myself, against the cabinet.”

Ghani said Afghanistan was in desperate need of foreign funds, and needed to assure donors that their money would be well spent.

Ghani and Cameron are to appear together at a panel discussion at the anti-corruption summit on Thursday. Before the event Cameron has attempted to counter claims that his campaign against international corruption is stained by London’s reputation as the money-laundering capital of the world by announcing that he was introducing a new corporate offence for executives who fail to prevent fraud or money laundering inside their companies.

The British Cabinet Office minister Matt Hancock said on Thursday that Ghani, as well as President Muhammadu Buhari of Nigeria, were coming to London “precisely because they want to deal with the corruption in their countries”.

He told Today: “As the president of Nigeria himself said, our prime minister is telling the truth about the scale of the problem, and this is the first time there’s been a global summit to tackle corruption, and frankly in the past the world has turned a blind eye to this problem. Just because it’s hard to tackle doesn’t mean that we shouldn’t.

“We’re going to take action at home so that people can’t hide their ill-gotten gains here. There has been a problem in developing countries for sure, but sometimes the gains wrongly made in developing countries have been hidden in the developed world including in the UK.

“Transparency is central to knowing where money has been hidden. Next month we’re going to publish the ultimate ownership of all UK companies, we’re the first G20 country to do that, and we’re announcing today that we’re going to make sure that anybody who owns property in the UK – there are about 100,000 properties owned by foreign companies – and anybody who sells to the British government, has to declare who the ultimate owner of that company is.”

Defending the UK government’s actions over its overseas territories, which will not be forced to create central registers of company ownership, Hancock said: “That would be anti-democratic, but what we have done is make a huge amount of progress in overseas territories, we’re now going to have a register of beneficial ownership, and we’re going to have an automatic exchange of that information with 40 jurisdictions, so that the authorities can see this ownership and take action.

“We want them to come with us on this journey and the vast majority of them have. There’s more progress with [the] Cayman [Island]s than you mentioned, and all the other territories are making progress and the key thing is the world has got to act together. The British overseas territories after the actions they announced this week will be more transparent than many developed countries including states of America and other countries in the European Union.”