The Prime Minister`s visit to Ankara comes at an unstable time for Turkey, which has suffered several terror attacks in recent months.

Mrs May will also be under pressure to confront Mr Erdogan over human rights, as his crackdown on dissent following last summer`s failed coup has seen thousands of officials jailed and several media outlets closed.

The UK and Turkey have agreed to set up a joint working group to pave the way for a free trade agreement, but formal negotiations cannot commence until Brexit is finalised.

Amnesty International has said that the human rights situation across Turkey has "deteriorated markedly" during the state of emergency imposed by Mr Erdogan - with the charity urging Mrs May to ask "probing questions" about allegations that those in detention have suffered ill treatment.

Downing Street has not confirmed whether human rights will be raised during the discussions, but a spokesperson said: "We have already expressed our strong support for Turkey`s democracy and institutions following the coup - but we have also been clear that we urge Turkey to ensure their response is proportionate, justified and in line with international human rights obligations."

Turkey is going to become the 13th country to set up a working group on trade with the UK.

On a visit to Ankara last year, Foreign Secretary Boris Johnson expressed hope of securing a "jumbo" free trade deal with Turkey after Brexit.

Figures from the International Monetary Fund show the UK was the second-largest destination for Turkish exports in 2015, buying more than £8bn in goods.

The Prime Minister and Mr Erdogan are also expected to unveil a strategic security partnership which will see the UK and Turkey collaborate more closely on aviation security and counter-terrorism measures.

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