//// The holiday ended June 30th //// That's not strictly correct. The rates change on 1st Oct 2021: https://www.gov.uk/stamp-duty-land-tax/residential-property-rates .... and as already stated, it's the time you complete that is important.
Is it going up? Is that when the holiday/reduction ends. Thought that had happened allready.
Anyway its calculated at the time of completion not when you start looking