I wrote to my MP, Tessa Jowell on 27 Sept, who responded immediately by writing to the Foreign Secretary. We have now had a reply (dated 13 October)
...We have checked with our officials in Damascus who have no specific information about this case. Although, they have heard that Mrs Carla Bruni-Sarkozy has taken an interest. Our Embassy in Damascus is following events closely and officials raise the issue of arbitrary detentions regularly with the Syrian Government. However, our capacity to lobby on specific cases, especially on behalf of non-British Nationals, is extremely limited.
[and handwritten addition:] But we will keep an eye on this, to see if there is anything we can do.
Signed Alistair Burt, Foreign & Commonwealth Office.