Prime Minister Boris Johnson told African leaders Monday that Britain would be more open to migrants from their continent after Brexit as he hosted a summit intended

to boost trading ties.

He also promised an end to direct UK state investment in thermal coal mining or coal power plants overseas, saying London would focus on supporting a switch to low-carbon energy sources.

Johnson was speaking at the start of the first UK-Africa Investment Summit in London, a clear pitch for business less than two weeks before Britain leaves the European Union.

After highlighting all that Britain has to offer, he said Brexit would mean an end to preferential treatment for EU migrants.

"Our (immigration) system is becoming fairer and more equal between all our global friends and partners, treating people the same, wherever they come from," he said.

"By putting people before passports we will be able to attract the best talent from around the world, wherever they may be."

Nigeria's President Muhammadu Buhari, who also attended the summit, said Brexit offered an opportunity for increased free trade across the Commonwealth -- and

said visas were a key issue.

"While many in the African diaspora enjoy considerable benefits from life in the West, they do not always feel at the heart of the community," he wrote in an article for The Times on Monday.

"A renewed sense that there are ties that bind us through the Commonwealth, and a concerted effort to grow those links through trade, could act as a spur to encourage togetherness and the certainty of belonging."

- Breathe the same air -

Johnson, whose country hosts the next UN climate change summit in Glasgow later this year, also announced a shift in investment strategy to help combat global warming.

Sub-Saharan African faces a number of environmental challenges, particularly the effects of climate change, water and air pollution, desertification, deforestation and over-fishing.

On fossil fuels, Johnson said: "There's no point in the UK reducing the amount of coal we burn, if we then trundle over to Africa and line our pockets by encouraging African states to use more of it, is there?"

"We all breathe the same air, we live beneath the same sky. We all suffer when carbon emissions rise and the planet warns."

He added: "Not another penny of UK taxpayers money will be directly invested in digging up coal or burning it for electricity.

"Instead, we're going to focus on supporting the transition to lower and zero carbon alternatives."

The British government's export agency reports providing £2 billion ($2.6 billion) in financing for UK company exports to Africa in the past two years.

The agency says it now wants to "increase its risk appetite" in Egypt and the emerging economies in Nigeria and Rwanda.

The UK government said the London summit will see British and African firms announce commercial deals worth £6.5 billion.

It did not spell out whether these were all firm commitments or included memorandums of understanding that do not always result in actual deals.

Britain will leave the EU on January 31, although ties will remain the same for 11 months while the two sides thrash out a new trading relationship.

The UK has said it will be leaving the bloc's single market and customs union.

Johnson wants the freedom to strike trade deals with other countries, even at the expense of some of its producers facing trade tariffs and quotas as a result.