Student visa, no reply after 3 month !!!

[engineer.hesam]

Hi all
I need your urgent help.
I have applied for my student visa on 28 Nov 2007 in Tehran and I have no reply from the embassy yet !!!. They say they have referred my application to London but I dont know why?
I am going to start my PhD in petroleum engineering in Heriot Watt univeristy. I have full scholarship for my studies and also a living stipend of 12600 GBP per year, tax free. ( so there is no problem with the money )
My supervisor has been following my visa application and even he has sent a fax to embassy.
Can any1 tell me what is the problem with my application and what I can do? Embassy still tells that you have to wait. but how much should I wait?It is for more than 3 month.
My start date was 1 Jan 2008, although my Prof has been mentioned in that fax that he is relaxed with my arrival date. ( it is a research degree , so there is no class)
I cant understand why it should take so long when you submit unconditional admission and full scholarship letters.
Please help me !!!

[SYH]

You are from Tehran. Why do you think it is taking so long?