What distance shall we keep from the vehicle in front of us when driving through a tunnel?

In a tunnel, when we do not intend to overtake, we must always maintain a safety distance from the vehicle in front of us of at least 100 metres or a minimum interval of four seconds. In the case of vehicles whose maximum authorised mass exceeds 3,500 kg, the safety distance to be kept from the vehicle in front shall be at least 150 metres or a minimum safety interval of six seconds.