Loft condensation even with ventilation

Each year my loft gets condensation on the north facing roof. I've tried the usual ventilation fixes and sealing gaps in the loft access etc). This seems to work to an extent but the issue still persists on very cold days (not happened yet this year, but I expect it will).

I also have an unheated conservatory on the north facing wall. I've noticed that on some cold days, the outside of the double glazed windows has condensation on it. Presumably the moisture content of the outside air is high enough to condense when it meets the cold glass. It occurred to me that the roof tiles will be just as cold as the glass (possibly colder as they are higher up). If that is the case it seems likely that the air inside the loft will have the same moisture content as the outside air and hence the reason that condensation forms on the roofing felt adjacent to the cold tiles. It might be possible that increasing the loft ventilation has increased the amount of cold air that is admitted. So it could be that one of the recommended fixes for the condensation might in fact be making it worse.

Any suggestions on how to avoid condensation in these circumstances?

You need a through draft in the loft to keep fresh air going through.
You need plenty of insulation in the loft to keep the warmth in the rooms below.
Make sure that the loft is sealed off so loft hatch needs to be air tight and any pipes or cables going through ceiling needs to be air tight.
Do you have a water tank in the loft?
That needs to be sealed with a lid and well insulated.

Have you watched this?

Thanks for your reply
You need a through draft in the loft to keep fresh air going through.
Yes - lots of through draft - added new vents.
As per my post, if the outside air sometimes condenses on the outside widows, surely it would condense on the inside of the roof (given that the air comes into the loft through the vents)?

You need plenty of insulation in the loft to keep the warmth in the rooms below.
Plenty of insulation too.

Make sure that the loft is sealed off so loft hatch needs to be air tight and any pipes or cables going through ceiling needs to be air tight.
New seal fitted last year - near airtight I'd say.

Do you have a water tank in the loft?
That needs to be sealed with a lid and well insulated.
Tight lid fitted, but the expansion pipe passes through the lid on the central heating header tank. Almost impossible to create a moisture proof seal. From another thread I have on this site, must plumbers install this way. Tanks are well insulated.

Did you watch video?
Says some moisture will be going through the plasterboard.
You can put a vapour barrier in to stop that.

Great video.

This thread mentions similar circumstances

Definitely warm air getting into the attic and not enough ventilation...

This morning my unheated conservatory has condensation on the outside of the glass. My original point was that if the glass is cold enough to cause condensation, and the same external air is free to circulate inside my loft why wouldn't it condense on the roof tiles (assuming they are just as cold as the glass)? More ventilation will only allow the same air into the loft.

What damage is it causing?

None as yet, but it sometimes drips onto the loft insulation. I'm worried it might cause mould though.