Windscreen steaming up

[Phuketpaul]

I've been having an issue with my car recently, every few minutes when driving along the front screen will fog up, quite often so badly that I have to pull over until it clears. If I set it to full defrost it will clear reasonably quickly, but will still mist up again soon after.

I've checked the plenum below the wipers is clear of leaves and is draining correctly, I've checked both of the air con drains, and both pollen filters are dry.

Any ideas?

[NotNormal]

Change the pollen filter and make sure the intakes are clear too

[Phuketpaul]

Change the pollen filter and make sure the intakes are clear too

I've checked the pollen filters and they look pretty clean and dry, only changed 4000 miles ago but new ones ordered.

The drains under the windscreen and either side of the transmission tunnel are clear, where is the actual intake?