Drilling into brick chimney. Confused

[Dan88]

Hi. Im Looking for abit of help. I have a 1960s terraced house with a brick built chimney. I removed the old gas fireplace some time ago and boarded the opening. I am putting a tv aerial in the loft and want to run the co ax down the chimney, trouble is I have drilled a 25mm hole through the centre of the chimney in the loft and have gone roughly 300mm deep and have not found the actual chimney flue. If I keep going I’m almost through to the other side. Does anybody know much about chimneys? I’ve attached an image. Thank you

 

[RandomGrinch]

Could there have been an upstairs fireplace as well as a downstairs one?
It looks wide enough for a second flue?

 

[Dan88]

Hmm I’ve not thought of that. I don’t think so. So you’re thinking there’s two separate flues and I’ve gone straight through the middle?

 

[RandomGrinch]

So you’re thinking there’s two separate flues and I’ve gone straight through the middle?

Maybe?
I'm afraid I'm not familiar with 60's terraces, but that would be the case with my 1890's one!
But for me, it's fairly obvious where the two flues go!

 

[Dan88]

Ah yes I can see by your picture.