Condensation in attic

In August I had my loft (storage area) re-insulated to a depth of 250mm under a subsidised scheme, after which I built up the joists to clear the insulation and re-laid the chipboard flooring in the central area. So far so good. I have now found that there is a considerable amount of condensation on the undersides of the roofing felt on the sides of the roof which don't receive any winter sunshine. The rafters are getting damp and I have found some signs of mould. Any ideas to sort this out will be welcome.

ventilate the loft. it may be that the insulation has been pushed to the edges of the loft and is blocking the eaves

look for the source of moisture - most likely it is coming up from a warm damp house below, especially if you drape wet washing on radiators, or use the bath/shower without running an extractor fan, or have holes in the ceiling, for example around downlighter, pipes, or an ill-fitting hatch.

it is possible but less likely that you have water-tanks in the loft with no plastic lids, or a plumbing fault causing hot water to rise up into them.

make some spacers out of timber, carefully insert these betwen the felt laps without damageing the felt. This will allow air to flow into the loft and hopefully stop the condensation.

if this works consider some vent tiles etc