Hi,
PIM4110 (Property Income Manual), clearly states that the conditions for a new let are applied for the first 12 months from when the letting began. There is a period of grace election and information can be found concerning this aspect at:
PIM4110 - Furnished holiday lettings: qualifying tests for 2011-12 onwards (IT and CT) - HMRC internal manual - GOV.UK.
If you wish to apply for the election, follow the instruction at:
PIM 4110
There is a time limit to make an application for a period of grace.
Thankyou.