<blockquote id="quote" class="ffs">quote:When arriving into the UK as an international passenger and continuing on to a domestic flight;
you are required to collect your luggage at the first port of entry to clear customs and immigration.[/quote]Not so!

Immigration - yes. Customs - not checked luggage in some situations.

As the OP states, your luggage can be checked straight through. I have landed at Gatwick(with AA from USA) and taken a domestic flight to Manchester with BA with my baggage not seen until Manchester.

That of course means that your bags don't clear customs at Manchester