The downgrading of remedial action to track defects as part of a trial of a newultra-sonic track-testing regime poses a serious safety risk to rail staff and passengers, according to the RMT (link below.)
http://www.rmtbristol.org.uk/2008/04/ultrasonic_inspection_trial_ra.html#more

They have asked the railways inspectorate to investigate the 12-month trial, already under way in northeast England.

The inspectorate is already investigating evidence gathered by the union that the ultra-sonic train misses some track defects altogether and should not be relied upon to the exclusion of other inspection methods.