Yellow staining

[ROY7E]

Hello,

Newly painted ceiling has caused this yellow spotting to come through the new paint in a small box back bedroom and on the landing ceiling.
House is relatively old with the previous owners not doing much in terms of painting.
After noticing the colour coming through, we have since scraped and sanded down some of the ceiling waiting until it's all dried more to do more scraping and sanding in hopes it will rid of it.

What sort of paint do I need / how to remove this?
Is it nicotine?
Any help appreciated

 

[RandomGrinch]

I may be wrong, but it looks to me as if it is previously cleaned, or developing mould spores, caused by condensation.
Have you checked to see if the insulation in the roof space is properly rolled out over that area, is an appropriate thickness and is dry?

 

[ROY7E]

I may be wrong, but it looks to me as if it is previously cleaned, or developing mould spores, caused by condensation.
Have you checked to see if the insulation in the roof space is properly rolled out over that area, is an appropriate thickness and is dry?

Thanks for replying but yes all insulation above is dry and appropriate thickness had it all checked and checked myself, boarding all seems fine from above also