Mould on roof timbers

Hi all
When I moved into my home about 6 months ago there was small amounts of white mould on the rafters in my loft, just running alongside the underside of the felt. Over the winter this has appeared to get worse.
Picture below hopefully

The mould appears to be very superficial and is only on the surface and can be brushed off fairly easily.

I have inspected the loft and it seems that insulation has been forced very far down between the rafters (we have a large loft conversion so the loft space is quite small with a long distance down to the eaves).

Could this be a ventilation problem? Could I reduce the mositure content of the air by using vent tiles, or is ventilation not the answer to this type of mould?

Any advice much appreciated.
Thanks


Ben

it`s definitely lack of ventilation - but at least you haven`t got "breathable" membrane - like new builds , where I predict loadsa trouble . so maybe you have eaves vents already and just need to move the insulation , as you suspected

Thanks for the reply

Will the timbers need treating once the ventilation is sorted or will any mould stop growing once air is flowing through?

I will check for eaves vents, if there are none are ventilation tiles suitable?

THis is a mid terrace, 180 year old house.