My friend and I are working in Riyadh. We are Filipino by nationality and passport. We have Schengen visas because we will be travelling around Schengen territories. On our return to Saudi Arabia, we will leave from Berlin, Germany and fly to London Heathrow for a 16-layoverhour layover before the flight to Riyadh.
Are we able to go outside the airport during the layover in the UK? What visa do we need to be able to tour a bit before our next flight?