Poland has a population which is 2/3rds that of the UK, but, it has a much older/poorer quality, housing stock. Whilst I disagree with Paxman on much of the artical, his comments on housing and affordability are unfortunately, very truthful.
Poland is quite different from the UK, UK has an older population who will want to trade down over time. Poland population die younger. It also sufferers from emigration not immigration. In Poland much of the older generation seems to have been given housing which they now own and there fore have savings to invest and assets to borrow against. You are also right that Poland, more than most other countries needs more stock.
However, these are longer (medium?) term trends, for now prices are not going up. The world banking crisis/Great Depression II is more of an influence.
^ "since 2007?" That seems to confuse the issue more than anything if the talk is about the trend this year...
Look at the trend on the chart yourself, its down everywhere, there is no debate on that.