I'm sure, you are talking about Barrets Dream start offer. What you've been told is a load of rubbish. There's no such requirement from Halifax as such, but some government sponsored schemes do have such requirement.
I personally know people who've recently been approved from Halifax wihtout ILR, but you do need to have at least 2 to 3 years residence left on your visa, thats all. If you are trying to talk to a Halifax branch then contact them drictly to their mortgage contact centre by phone (check their website for the phone no) thats your best chance of securing a mortgage, coz the people over there are professionally qualified to do this job, not like branch junkies.
Another option is to try through the IFA broker recommended by the builder. Are u based in London. or outside...if you need any further assistance...do let me know.