A former Nigerian oil minister accused of being treated to luxury home stays and lavish spending sprees in the UK in exchange for granting government contracts has denied asking for or taking bribes.

Diezani Alison-Madueke, 65, told Southwark Crown Court on Monday that she had "tried to push back on corruption" in a country plagued by it since the days it was a British colony.

Several Nigerian businessmen are alleged to have bankrolled huge spending sprees, including more than £2m at luxury store Harrods and £4.6m on refurbishing homes in London and Buckinghamshire.

But the ex-minister said that the cost of services laid on for her while on official duties were later repaid.

"I can state categorically that at no point did I ask for, take or receive a bribe of any sort from these persons and did not abuse my office," Alison-Madueke told the court.

"I always sought to act impartially".

She said money spent on her behalf was reimbursed by the state-owned Nigerian National Petroleum Company (NNPC), adding that a service company was set up in London to handle the logistics because the financial structure of the NNPC was in a mess.

"They paid for all my hotels, chauffeurs... to allow me to perform the job that I did," she said.

The prosecution's case is based on allegations that Alison-Madueke was given access to a "grand" home in Buckinghamshire, a £2.8 million home in Marylebone, and multi-million pound homes overlooking Regent's Park, and allegedly benefited from renovations valued at £4.6m.

The court heard how she and her extended family spent five days over Christmas 2011 at a house in Gerrards Cross, Buckinghamshire, because her ex-husband required hospital treatment and could not fly back to Nigeria.

She said she was not involved in the arrangements for the stay.

A second visit, she said, was over two weeks when she and 10 to 12 officials wrote a book praising the Nigerian president's championing of women.

"I took it upon myself to put together that book to showcase what he did for women," she said.

Alison-Madueke said another property overlooking Regent's Park was used for "discrete" official meetings, while she said another property she is accused of using was "completely gutted" for renovations and unusable when she saw it.

The court had previously heard how Alison-Madueke and her mother stayed in two apartments in St John's Wood with the rent being covered by Nigerian businessman Kolawole Aluko. He is one of several Nigerian businessman involved in the case who are not on trial.

Alison-Madueke said she had suggested this was much cheaper than continuing to hire £2,000-a-night suites in expensive hotels like the Savoy and Dorchester.

In court on Monday, the former minister said she was not aware at the time that one of her chauffeurs had delivered £100,000 in cash to her, adding that the money had had nothing to do with her.

The court heard how Alison-Madueke had risen quickly through the ranks at Shell, becoming the first senior female executive in its Nigerian operation.

This was despite her not wanting to work for the multinational company because of its treatment of her father, she said, who had once also been a senior employee.

"I found the job uncomfortable to put in mildly, " she said, explaining that her father, who was a tribal leader, had once unsuccessfully taken legal action against Shell "for apartheid practice in West Africa."

She told the court how when she worked at Shell, the company was having big problems dealing with oil spills in the Niger delta area where her family was from. She didn't believe the company had done enough "to make good on the devastation that they had caused".

Asked about concerns with her own security, she said Nigeria was a "very patriarchal society" so to have a "woman sitting at the helm was a major no no."

She added that she was "under dire threats of kidnap" and that members of her family had been seized.

The court also heard how in 2015, Alison-Madueke was elected the first female head of the Organization of the Petroleum Exporting Countries (Opec), a group of oil-exporting countries which meets to decide how much crude oil to sell on the world market.

Alison-Madueke denies five counts of accepting bribes and a charge of conspiracy to commit bribery.

Also on trial, oil industry executive Olatimbo Ayinde, 54, denies one count of bribery and another count of bribing a foreign public official.

Meanwhile, Alison-Madueke's brother, former archbishop Doye Agama, 69, denies conspiracy to commit bribery.