Hi and welcome....know u r not alone, even in the UK as there are Drs that do know and treat Chiari....have u looked at the list for the Ann Conroy Trust?
Use this link to locate a list of Chiari Drs and there is a link to the list for the UK....
http://www.medhelp.org/health_pages/list?cid=186
May I ask what symptoms u r experiencing and how u r feeling? Many of us have had children b4 getting our DX so it is possible, but again, it all depends on how u r doing now b4 u get pregnant....some suggest u have C sections to prevent the bearing down and strain of natural childbirth.....not saying it can not be done, but it can trigger ur Chiari to worsen.
Try and look up Drs from the Trust to see if they can do more testing to see if u can have a safe pregnancy .