A recent survey suggested improving air ventilation in the roof space, how would you go about acheiving this?

Installing vented ridge tiles and removing solid soffits and replacing with vented soffits is whats required, May I ask why the ventilation is necessary? Do you have damp?

You could install soffit vents, but more effective to fit roof vents, you can get them to match your slate/tile. On a standard 3 bed property we would fit 8no, 4 on each side, with 2 at low level and 2 at high level. Make sure whoever fits them cuts through the felt, as I have seen them fitted without cutting the felt, you need to vent the main roof space and have a good air flow.

Post as a job for quotes on vents in your soffit/fascia

You could do this via your soffits depends if they are would or plastic, you can plastic soffits with vents etc Hope this helps

Sweating roofs are a symptom of not having breathable felt on your roof. A cheap and simple solution to this is to have roof tile vents fitted which will allow the roof to breath