EU and UK Customs is very different process from US. Arguably more intelligence led.
UK domestic then adds another level of complexity. Bags off domestic flights used to come to 2 different belts in GLA depending on the origin, but that has now ended and the bags all arrive together. It is up to you to declare anything that needs declaring via the red phones. That can be done at LHR and MAN.
If you are interested, there is a multi mage thread on UK customs in the UK destination forum discussing where and when you (or your bags) have cleared customs.
Have I Cleared Customs ?