echinosum writes
The largest subsidence risk results from the combination of
(1) deciduous trees
(2) clay soils
See for example
http://tinyurl.com/qhkzz5

Thank you - a heartwarming link (for someone in a clay soil which is not
London clay, in a pre-1900 house which is not detached)

" * Detached properties have a greater susceptibility to subsidence
or heave damage than non-detached properties.
* Properties built prior to 1900 are less susceptible to damage than
those built thereafter
* London clay is, by far, the most commonly encountered "problem"
soil.
* It typically takes about 50 years between construction and
perception of damage, while only about 6% of cases occurred in the first
10 years after construction.
* The likelihood of a property being underpinned following damage
generally increases with the level of damage
* Oak trees are, by far, the most damaging species of tree. "

Still feel I did the right thing in persuading the Church to cut back
their beech tree (3m from our house) so that its branches no longer
sweep our roof tiles ;-)
--
Kay