According to Fars, the semi-official news agency of Iran, a number of British soldiers have been captured in Syria by the forces of Bashar al-Assad. As the article reports:

A number of British military men were held captive by the Syrian army in Eastern Ghouta of Damascus, media reports disclosed on Wednesday, saying that they had infiltrated the region for the last month US plot to attack Damascus in collaboration with terrorists and NATO forces that failed.
The Arabic-language al-Mayadeen news channel’s correspondent in Moscow reported that a number of British forces have been captured during the military operations in Eastern Ghouta.
Earlier reports had disclosed last month that foreign military forces were deployed in Eastern Ghouta of Damascus to launch a ground assault against Damascus in cooperation with the US.
The US and Israel planned to launch attacks on Damascus from several fronts in collaboration with the NATO and Jordan, but the plot failed after the Syrian army scored rapid, major victories in Eastern Ghouta.
Informed sources disclosed that the US and Israel intended to support the terrorists in Eastern Ghouta by airstrikes so that they could capture vast areas of Damascus to pave the ground for the Syrian government’s collapse.