After we became aware that Syrians with valid entry visas to the UK were being denied exit from Turkey, we contacted the Turkish embassy in London and the British embassy in Ankara and the issue seems to have been resolved. Syrians with UFF forms (forms for affixing the visa) should now be able to leave Turkey to the UK.
Letter from British consulate in Ankara:
RR participated in a candle light vigil hosted by the Muslim Association of Britain in Picadilly Gardens in memory of Sheikh Abdul Hadi Arwani who was murdered in London on 7 April 2015. We sent our condolences to family and friends and called for a speedy investigation as well as the delivery of justice.