Frustration

Some time ago I was helping a client at a police station in London. The police were quite happy to use my services over the counter, where I spent over hour interpreting between my Polish client and the police. However, when it came to making a formal statement, the police insisted on using their own interpreter, even though I was a fully qualified interpreter, listed on the NRPSI and I have the Metropolitan Police Test certificate for interpreters. The problem was the fact that I was not listed on the Metropolitan Police list of interpreters. I must admit, that list is virtually impossible to get onto. I meet the criteria but I do not know what else I can do to be included.
Anyway, that Polish person, who happened to be a lady with a baby, had to wait at that police station for 4 hours for another interpreter to turn up, even though there was a qualified interpreter already present. Where is the sense in that?