http://www.ft.com/cms/s/0/47931550-f874-11dd-aae8-000077b07658.html

Reading this article, I was wondering whether the two statements
"Even under what seem like extreme scenarios for UK and US house prices, many people agree that few mortgage bonds outside subprime definitely look expensive. "
"Also, for example, Fitch Ratings recently said that under its stress testing, which included the assumption of a 30 per cent fall in house prices, no mortgage bond rated triple A in the UK would see a downgrade."
are linked. In particular, is 30% fall in house prices considered to be an extreme scenario?  I belive the 30% reflects a peak to trough estimate

http://www.ft.com/cms/s/0/8305276e-ebdf-11dd-8838-0000779fd2ac.html

yet when the derivatives market are pricing in 46% peak to trough,

http://www.tfspropertyderivatives.com/pdf/RISK&MANAGE/2009/Feb-09.pdf

30% seems very optimistic.