You are always entitled to speak with the CIO (Chief Immigration Officer) on Duty, although the wait may sometimes be a few minutes or longer especially at peak periods at busy ports.

I've entered the UK approx. 150 times over the last few years as a visa national and the only 2 times that I was hassled were by the same officer at Gatwick, albeit a couple years apart.

In the first case, a call to her boss (an old friend of mine) sorted things out very quickly with an apology. The officer made some derogatory comments about the poor standard of documents issued by my country of citizenship to which I had responded that she should confine her editorial commentary to UK Immigration Law and leave other countries' domestic policies to the Foreign Office. This resulted in a retaliatory consignment to the sin bin until I was able to call her boss on my mobile and he organised my safe passage without further ado.

In the second case, the same lady was working a random departure check and tried to mess with me since I had entered the UK as a crewmember the previous day and did not have an entry stamp or IRIS receipt. I recognised her but she did not recognise me initially, until she asked me to stand aside and I responded with "do you really want me to get Dave* involved again Martha*?" (* names changed). A look of realisation hit and she grudgingly gave me the passport back and waved me along.

As a liaison officer for an airline that deals with UK Immigration, I deal with dozens of passenger complaints about allegedly rude officials every month, but I have also found that the ones that are forwarded to the CIOs for review invariably result in a decent investigation being conducted and usually responded to within a couple months.