Securing 40 trade deals with Kazakhstan worth £3 billion was "not bad for one afternoon's work", David Cameron declared after talks with the country's president.
The Prime Minister said he saw Britain and the oil and mineral-rich central Asian state as " partners in prosperity and partners in progress" as he oversaw a signing ceremony at the Foreign Office alongside Nursultan Nazarbayev.
Downing Street said Mr Cameron raised the issue of human rights with his counterpart, who was recently re-elected with 97.75% of the vote and is regarded by critics as an autocrat.
Mr Nazarbayev insisted he was committed to widespread reforms including ending corruption, improving the justice system and ensuring "an open, liberal government that is accountable to the people".
But the visit - which came a fortnight after the red carpet was rolled out for a trade-focused state visit by Chinese president Xi Jinping - was criticised by human rights activists.
Amnesty International UK's head of policy and government affairs Allan Hogarth said Kazakhstan had "a terrible track record over the torture of criminal suspects and in crackdowns on peaceful protesters and journalists".
"Pursuing contracts with oil and gas-rich countries like Kazakhstan must not come at the cost of silence on human rights abuse - this should never be part of the deal."
Labour former prime minister Tony Blair has been a prominent adviser to the regime.
Mr Cameron pointed to deals involving four new gas plants and a steel production facility in Kazakhstan as key components of a widening partnership, suggesting the latter could benefit the UK's own crisis-hit steel industry.
"By bringing together our two diverse economies, broad international co-operation and shared commitment to reform, I believe our relationship can become even stronger," he told Mr Nazarbayev.
They were "e xtending relations into all sectors", he suggested, painting it as the fruit of his visit to Kazakhstan in 2013 - the first by a serving British premier.
Mr Nazarbayev said his country was diversifying its economy as it faced a "time of crisis" in the oil prices, using financial reserves from revenues built up in previous years.
There had also been agreement, he said, to daily flights between the UK and his country.
The president said he was happy to co-operate with Mr Cameron on global issues such as Ukraine and relations with its two giant neighbours, China and Russia.
"I always inform him as much as I can but I always remind him: let's not forget what London should for for Kazakhstan," he told business leaders and politicians at the event in the Foreign Office's opulent Locarno Suite.
"We are not asking for anything. What we are asking is just, 'come over, do your business, earn your money together with us'. We welcome the business and we are creating exceptional conditions for this."
He told Mr Cameron: "I congratulate you on winning the last election. You have carte blanche now to carry out completely new policy.
"I hope that in this policy there is going to be some place for Kazakhstan."