I've had 'seek assistance' ever since I got my latest (blue) passport. Same on every UK entry, tried the various techniques above. Chip is fine, works abroad. I've been asking border staff and get variations of nothing through to 'you have a common name' which I'm convinced is the official fob-off as is distinctly not true of my surname (only a few dozen of us in the country).
Contacted Passport office and got told to send it in for inspection (I haven't, I can see the chip is working fine, I need a passport).
Looking at other ideas - anyone tried a home office subject data request or an FOI to see if that reveals anything that might help?