Lets Aviat,
With regards to the deportees. The airline has no say on these or how many escorts they have. Some deportees require no escorts, they are usually ones who are returning because they have been asked to or have handed themselves in under some kind of amnesty, or they have just been refused entry to the UK and are going back on the next flight the airline which bought them in has.
1 or 2 escorts may take along someone who is less willing to leave but isn't considered a danger to others and the situation you described with the 6 seats being used would to me sound like a prisoner being deported back and to ensure safety they have enough security around them so they don't do a runner or kick off.