Turnitin have informed us that the service is back to normal.  There was degradation which may have meant users were unable to view submissions and/or similarity reports, or may have experienced slowness when accessing the service between the following times:

Wednesday 9th December: 15:13 – 21:30 GMT.

Apologies for any disruption this may have caused.  Further information is available on the Turnitin service status page.