Britain is bargaining with one of the world's most brutal dictators because we need to use his country as a transit route to bring thousands of tons of military equipment home from Afghanistan.

Senior officials admitted yesterday that Uzbekistan's President Islam Karimov had the UK "over a barrel", after his country emerged as the favoured route home when British forces are withdrawn from Afghanistan by 2014.

Britain, along with the United States, has stepped up diplomatic contacts with the Karimov regime in recent months, and the Defence Secretary, Philip Hammond, visited the Uzbek capital, Tashkent, for talks on supply lines in February. The Independent on Sunday understands that "exchange visits" by senior defence officials from both countries will take place in the coming months.

Campaign groups condemned the developments – which threaten to compromise David Cameron's commitment to human rights – and urged the Government not to "cosy up" to a man accused of presiding over torture, religious repression and forced child labour. The regime is also held responsible for murdering its own people, including the notorious Andijan massacre, in which government forces killed hundreds of protesters, most of them unarmed, in 2005.

But the Prime Minister was warned he could pay a high price for securing Mr Karimov's co-operation, with a demand for him to visit Uzbekistan – and for Britain to invite the Uzbek leader for a state visit. Craig Murray, a former British ambassador to Uzbekistan, also claimed Mr Karimov wanted leave to install his daughter, Gulnara Karimova, as the Uzbek ambassador in London. Ms Karimova, 39, was named in secret cables by US diplomats, revealed by WikiLeaks, as "the single most hated person in the country" with an "unquenchable thirst for money and power".

Steve Swerdlow, Central Asia researcher for the campaign group Human Rights Watch (HRW), said: "It's not in the interests of the UK to cosy up to one of the most repressive governments in the world, which is truly fragile, unstable and one day will likely implode or explode."

John Dalhuisen, of Amnesty International, said: "The talks will not come without cost or very severe embarrassment to the Government if it wants to continue to promote itself internationally as standing behind those fighting against corrupt and human rights-abusing regimes, because this is among the worst of those kinds."

Mr Karimov was regarded as a pariah by the international community for most of his 22 years in control of his country. However, amid growing fears that deteriorating relations with Pakistan could scupper attempts to shift thousands of Nato armaments and armoured vehicles back to their home countries, Uzbekistan is now seen as the next-best option.

Some Nato powers have begun lifting restrictions on Mr Karimov and opening negotiations which critics claim could end up cementing the President's position and enriching members of his family.

Mr Hammond and the armed forces minister, Nick Harvey, toured five Central Asian republics to discuss expanding the so-called "northern route" for supplies to leave Afghanistan. The Ministry of Defence confirmed Mr Hammond held "a series of meetings with senior figures of the Uzbekistan government". Ministers revealed last month that Uzbekistan receives UK funding for activities that include the training of military officers in Britain.

A senior FCO source said: "Karimov does seem to have us over a barrel." A minister added: "If the Uzbeks ultimately say no, there are alternatives. But it would be much harder... it is worth trying to keep them on board."

Biography: 'The worst of the worst tyrants'

Uzbekistan's President Islam Karimov is one of Central Asia's most autocratic leaders, running a repressive regime that cracks down on any form of opposition. Mr Karimov, 74, was born in Samarkand and raised in a Soviet orphanage. He became president of an independent Uzbekistan in 1991. He has clung tenaciously to power since then through a series of what international observers have called "unfair and fixed" elections.

Critics accuse him of ruling with an iron fist, cracking down on protesters, sanctioning human rights abuses and routinely using torture on political prisoners.

Married with two daughters, he has been described as "the worst of the worst dictators" after his regime was accused of boiling two people alive.

Lene Wold

Q&A: Why Uzbekistan?

What do we need to move?

Britain needs to bring back approximately 11,000 containers of equipment and 3,000 armoured vehicles from Afghanistan, according to the Defence Secretary, Philip Hammond. This includes armoured patrol vehicles, tankers, trucks and weaponry such as heavy machine guns, mortars and rocket systems.

Why do we need a route out of Afghanistan?

With the 2014 deadline for withdrawal approaching, Britain must plan now for this "major logistical operation". Previously, equipment went through Pakistan to Afghanistan but repeated Taliban raids forced planners to examine alternatives. This accelerated when Pakistan closed the border crossing from Karachi to Afghanistan last November after the US killed 24 Pakistani soldiers on the border by mistake.

Why Uzbekistan?

Uzbekistan borders Afghanistan to the north and the two countries are linked by Afghanistan's only major railway – from Mazar-i-Sharif to the border town of Hairatan. It would enable weapons and equipment to be shipped north out of Afghanistan and through Uzbekistan.

Aren't there any alternatives?

The frosty relationship with Pakistan pales in comparison with the glacial links with Iran. Trundling tons of military hardware through a country which could soon be at war with Nato members is unthinkable, as is the prospect of taking kit through China. The other two states adjoining Afghanistan, Turkmenistan and Tajikistan, are not ready for the scale of convoys Nato needs to bring.

Has everyone decided on Uzbekistan?

The Americans – as well as the British – have courted at least five Central Asian republics, but Uzbekistan remains their favourite. Secretary of State Hillary Clinton leads the list of US political and military officials to visit Tashkent in recent months, but officials from Germany, Latvia and Poland have also made the trip. Italy signed an agreement with Moscow to secure the transit of military hardware via Russian airspace. France's defence minister, Gérard Longuet, favours the route through Pakistan.

What happens next?