I was talking to a friend (UK Born) a few weeks back that tried renewing online, he got a letter from them saying he would have to come in for an Interview and bring in any Proof of Identity to proceed, no explanation as to why, but he is guessing its due to hes earlier Passport running out over 9 years ago.
Anyway off he goes into London for the interview, and gets asked all sorts of questions, including Employment Status, Tax and NI details, driving Licence info etc, the sort of stuff you would expect but then came some really awkward questions that he was struggling to answer due to his age, some included, where did he take his driving test and can you remember the name of the Instructor, address of first job, Name of first Doctor and address of the GP, any Uncles, Aunts and or Nephews that have died or moved overseas, Countries that you visited that have required a Visa, Armed Forces or applications to MOD type jobs, Post Office, Telecom Government Job applications, School and College details, Dentists, Unemployment details since starting work, and so and so.
Cut a long story short he did up up with his new Passport but said, you would not believe what info these guys have on you or kept over the years.