With regards to Tinstaafl's journey from Brisbane to Manchester, it's worth remembering that bags will very rarely (definately not in the UK anyway) be transfered from an international flight to a domestic flight (they will be transferred vice-versa).
This is because bags on an domestic flight are not subject to inspection by Customs & Excise. Therefore, in the sameway that you will need to clear Immigration when you arrive in the UK, your bags will need to clear Customs.