Chris - and looking at Persimmon's annual report, I find the primary reason for the "55 percent upsurge in pre-tax profits" reported by Inside Housing on 28th February according to Tony, was a change in the valuation of their land-bank:
"During the year, the Group reviewed the net realisable value of its land and work in progress carrying-values of its sites. This resulted in a net reversal of the previous write-down of inventories of £13.3m (2010: £80.2m)".
There was also a significant reduction in their interest charges from £33.2m to £4.9m, helping to improve operating profit margin from 8.2% to 10.0%.
Their housing output was virtually the same as the previous year, at 9,360. Average selling prices dropped 2% due to an increase in the number of smaller homes being sold and a corresponding increase in the first-time buyer market.
This does not sound much like the business model you describe either.