To try to tackle this, the Welsh Labour government, alongside Plaid Cymru, introduced measures to curb second-home ownership. This included giving councils the ability to push council tax on second homes to 300% the usual rate. They also closed a loophole whereby second-home owners could register as a business in order to pay the much lower business rates.
Gwynedd council used these powers to hike council tax to 150% in April 2023. By the end of 2024, house prices had fallen by 12.4% as second-home owners tried to sell up. In Pembrokeshire, house prices fell by 8.9% after the council increased the council tax to 200% on second homes (though this was reduced to 150% recently).
Most places have a specific occupancy duration to qualify as a primary home, right?
If not, that seems to be a good option. Primary counts if used by owner for living >240 days of the year (random number but figured it should be at least 3/4 a year or so). Like how we calculate whether someone counts as in state vs out of state for tuition.