Where I used to live (North London) you were not allowed to find out the sex at an nhs scan! but we paid to have a sexing scan at a private clinic at 25 weeks - it only confirmed what I already knew - a boy! we even got a scan pic of his lil privates to prove it (bless).
I want to find out this time too - but should be able to at the normal nhs 20 week scan as I have now moved!