David Cameron is expected to urge all G8 leaders to commit their countries not to pay terror ransoms in an international effort to cut off extremists' funding.
Up to 70 million US dollars (£45 million) is estimated to have been paid to secure the release of Western captives in the last three years alone - an average 2.5 million US dollars (£1.59 million) per victim.
Much of that is believed to have ended up in the coffers of terror groups including al Qaida and its affiliates and the Taliban.
The UK outlaws such payments but other countries - including some within the group of leading industrialised nations - continue to meet the demands to the frustration of non-payers.
G8 nations have agreed a joint position on Syria at a summit in Northern Ireland, which could pave the way for fresh peace talks in Geneva.
If the body language between Presidents Obama and Putin is anything to go by, this summit has been a disaster.
David Cameron is unlikely to change his stance on backing 'moderate' Syrian rebels but there is genuine uncertainty as to Obama's plans.