As a regular visitor to UK immigration detention centres, I know that they’re places that you wouldn’t want to spend an hour, let alone stay overnight. (In fact people can be held for weeks or months The UK is the only country in Europe that doesn’t have a time limit on detention — and we’re talking about people who haven’t committed a crime!) Your experience is certainly amongt the more bizarre stories that I’ve heard, but I’ve come across people who’ve been detained for similarly absurd reasons. It’s good that you managed to get away that same day, but it’s a shame that this (understandingly) makes you determined not to want to return to the UK.
With impending Brexit, I fear that stories such as yours will be more and more common. You were told that the problem was that your honorarium was being paid by a German company. As both the UK and Germany are (still) in the EU, this should have made not a blind bit of difference — and for the UKBA to distinguish between companies in the two countries would have been clearly illegal!
As for lying to immigration officials, I’m afraid that they invite it. Not too long ago I visited an African country governed by a paranoid, quasi-dictator. Because I was travelling as a journalist, I decided to lie about why I was visiting–getting a visa otherwise would have been hard or impossible. When visiting the US, I’m regularly tempted tell half-truths because pretty-well all Homeland Security officials that I’ve been faced with have been so unpleasant. I see that the main problem with lying isn’t a moral one but a practical one — it’s hard to remember lies, but (if you’re not exausted) easy to recall the truth.