I’m using a vapour permeable underlay but using mechanical fixings with the ridge and hip tiles in conjunction with mortar because it is a conservation area. Do I need any other ventilation products?

The use of this type underlay allows the level of ventilation provided to be reduced, not omitted. The continuous 10mm equivalent opening at the eaves in conventional cold roof construction can be reduced to a continuous 7mm equivalent opening for a normal ceiling, or down to a 3mm continuous opening equivalent for a well-sealed or ‘continuous’ ceiling. This is not work usually carried out by the roofing contractor.