We still await confirmation of the exact changes to buy to let stamp duty (and all none primary residents purchases). Although the changes were announced in the Autumn Statement they have been subject to a consultation period that is now over and we await the final change confirmation that may not come till the George Osbourne delivers his budget on March 16th.
However, it does appear that one of the first assumptions may have changed. It appears that although a purchase of up to £40,000 will still attract no stamp duty, a purchase over this figure but below £125,000 may attract stamp duty at 3% on the full amount. Not just the amount over £40,000 as first presumed.
Watch this space for updates or alternatively you may have to be glued to BBC Parliament at 12noon on 16th March like the us!