Find a basement wall that backs onto a suitable yard (owned by the client)
from outside, dig a hole and form a concrete 'box'.
At ground level raise the 'box' by 150mm to form a ledge or 'upstand'
At basement level 'break in' to the basement to form a 'communication pathway'.
At outside ground level build a weathering skirt that goes over the 150mm high upstand.
The skirt should comprise of a duct with a louvre in it to let in (or exhaust) air.
At basement level you may use the new connection as natural ventilation or add a fan for mechanical ventilation.
voila
(I've done this quite a few times with no problems.)
good luck and use a good builder...make sure the new concrete box is suitably weatherproffed and waterproofed
Friar Tuck of Sherwood