Savills have copied my workings.

From City AM:

House prices are expected to surge another £50,000 over the next five years, further reducing affordability in the UK property market, according to new forecasts published today. Estate agent Savills predicts house prices will jump nine per cent this year, driven by the extended stamp duty holiday and prospective buyers rushing to purchase larger homes with gardens...

This explanation is pretty feeble - the SDLT breaks are being phased out and more demand for large gardens means less demand for small or no gardens, so should cancel out.

They then let the cat out of the bag - it's just a credit bubble:

Lower interest rates, an increase in the supply of high loan-to-value mortgages as lenders return to riskier sections of the market and high levels of savings built up during the pandemic are expected to keep demand elevated, Savills said.

Which is exactly what I said here. Going by the previous two 18-year cycles, a further increase of £50,000 before it all *pops* again is on the lower side of expectations.