British air strikes in Syria have killed or injured just seven Islamic State fighters, according to estimates released by the Ministry of Defence.
David Cameron won the support of MPs for strikes against IS in its Syrian strongholds in December, but the MoD figures show by the end of January just four attacks had resulted in the jihadist group suffering casualties.
None of the strikes involved the high precision Brimstone missile which was cited by the Prime Minister as the kind of UK asset which would make a "meaningful difference" to the coalition's battle against IS in Syria.
The RAF's operations against IS in Syria have focused on targeting the infrastructure used to support the group, including the oil fields which are a major source of revenue for the militants.
MoD sources said strikes targeting IS fighters were only carried out if there was no risk of civilians being injured.
Details of the estimated casualties were released by the MoD in response to a Freedom of Information request by the Huffington Post UK.
An attack on Christmas Day near Raqqa - the city dubbed the "head of the snake" by Mr Cameron because IS has its main headquarters there - saw one militant killed or injured by a Hellfire missile.
An MoD update for December 25, 2015 said an RAF Reaper struck an IS checkpoint south of Raqqa with a Hellfire missile.
Two more fighters from IS - also known as Daesh - were hit on the same day in Tabqa, also with a Hellfire.
On January 11, two fighters were killed or injured in a Hellfire strike in Al Busayrah, the figures showed, while two more were hit by a Paveway IV guided bomb on January 15.
A spokeswoman for the MoD said: "We are playing a crucial role in a campaign that will take time and patience. Using the right weapon for each scenario, RAF jets have struck Daesh almost 600 times.
"In Iraq we have helped to drive them out of Sinjar and Ramadi. In Syria, we have severely weakened them by targeting their key infrastructure."