UK Prime Minister David Cameron is set to travel to Turkey on Tuesday where he will meet with Turkish President Recap Tayyip Erdogan to discuss the Britons travelling through the country en route to the conflicts in Syria and Iraq.

The UK has already said it was facing its greatest ever national security threat. Britons returning from the conflicts in the Middle East, battle hardened and experienced in the use of weapons, could potentially launch attacks in the UK.

Turkey's long, porous border with Syria and Iraq has provided the main gateway for foreign fighters that want to join rebel groups in the countries.

"The focus, particularly given current events in Syria and Iraq and in that region, will be CT (counter terrorism) and Isil (IS,)" Cameron's spokesman said on Monday.

The intelligence community believes that around 500 Britons have travelled to the region, using Turkey as a transit destination, while around half of those are thought to have returned to the UK.

Two British men were jailed for 12 years and eight months each last week, after they were found guilty of engaging in conduct in preparation of terrorist acts.

"Certainly people travelling overseas from the UK to take part in terror activity is very much part of that relationship we have with (Turkey,)" Cameron's spokesman said.

The British PM will first meet with his Turkish counterpart Ahmet Davutoglu in the Turkish capital Ankara, before spending the evening with Erdogan.