Statistics on the use of language services in courts and tribunals

Statistical bulletin, 30 January 2012 to 31 January 2013 
http://www.justice.gov.uk/statistics/courts-and-sentencing/language-services-in-use

[…] 
Complaints 
During the period covered by this bulletin (30 January 2012 to 31 January 2013), there were 6,417 complaints recorded relating to completed requests made. The majority of the complaints came from tribunals (4,050 complaints, 63 per cent), with the most common reason for complaint being that the interpreter was late getting to the assignment (970 complaints, 24 per cent of complaints from tribunals). At criminal courts and prisons, the most common reason for complaint was that there was no interpreter available (35 per cent of complaints by these requesters). 

The complaint rate (the number of complaints divided by the number of completed requests) has increased between August 2012 and January 2013

Read more here: http://www.justice.gov.uk/statistics/courts-and-sentencing/language-services-in-use