Immigration questions on entering UK

[BenDToy]

On returning from a recent trip, the immigration officer at passport control asked me where I had arrived from. I initially refused to answer - I pointed out that my passport allowed me access to the UK and her role was merely to establish whether my passport is genuine, and whether it is in fact my passport. She insisted that she had the right to establish where I had been, and I believe she does not Am I correct?
I am prepared to be proven wrong, but please don't berate me for taking a stand. I know it may seem pedantic and argumentative, but there is an important point of principle at stake, in my opinion. She overstepped her authority by accessing for additional information which was not required.

[BenDToy]

Thanks spudqueen for actually answering the question rather than lecturing me about something I had already confessed to.
Thanks to all others for your responses as well. I have nothing to hide and I actually can't remember where I had been. Certainly nowhere to attract suspicion but I travel overseas regularly on business so it could have been any number of places. Only a very few of these destinations require API, and it is quite possible that they did not know where I had been. And with Schengen, it is virtually certain that I could have been in other countries without any records. And no she wasn't just making conversation.

[Trotbot]

Most law enforcement officers are entitled to ask any questions relevant to their jobs, which would certainly include information about where you had been. When I was in HMC+E we could ask pretty much anything, and we did, so unless UKBA has substantially less powers (which seems unlikely) then the Officer was right.

[trt]

'' I have nothing to hide and I actually can't remember where I had been ''.

Oh come on Bendtoy, you must have some idea where you have been, what is your status, are you from the UK or from another Country?

[BenDToy]

A couple of further comments.
As spudqueen confirmed, she was exceeding her authroity. Possibly not by asking the question, but by insisting that I answer it.
trt - I genuinely cannot remember where I had been. It was a month or so before posting the question and I travel frequently, but probably it was either, Norway, Denmark, Holland or Germany. Although I had also been to Sweden and Belgium around that time. I was just not sure which particular trip this happened on.
I am a UK citizen, I am perfectly respectable and have absolutely nothing to hide. If I was not a UK citizen, then I think the officer would have been perfectly entitled to ask where I had come from.