Originally Posted by
geronimo
There is transit security in T4S. Your actual transit route within T4S will depend on whether you are entering/leaving Schengen on either flight which would also require you to pass through passport control.
This page explains the various
Iberia - Connections at Madrid Airport
That page still seems to indicate IB flights to the UK leaving from T4 main. That is no longer the case and they are also out of T4S.
Also, there is a non-Schengen transit security in T4S as well.