That is so simple and perfect, thank you very much!!
I was halfway there, I had already put my html directly into _ColumnsThree.cshtml, but didn't realise I can just call a topic to be displayed, thanks nopCommerce!
So in summary again for anyone else I have done the following
In
Nop.Web -> Views -> Shared -> _ColumnsThree.cshtml I have added
inside the <div class="master-wrapper-leftside-3">
@Html.Action("InfoBlock", "Common")
<div class="clear">
</div>
//New code
@Html.Action("TopicBlock", "Topic", new { systemName = "LeftSideAdvertising" })
<div class="clear">
</div>
//End new code
@Html.Action("ManufacturerNavigation", "Catalog", new { currentManufacturerId = currentManufacturerId })
<div class="clear">
</div>
and inside <div class="master-wrapper-rightside-3">
@Html.Action("MiniShoppingCart", "ShoppingCart")
<div class="clear">
</div>
//New code
@Html.Action("TopicBlock", "Topic", new { systemName = "RightSideAdvertising" })
<div class="clear">
</div>
//End new code
@Html.Action("NewsletterBox", "Newsletter")
<div class="clear">
</div>
I also applied the leftsideadvertising code to _CollumnsTwo.cshtml for consistency between pages.
Then I have created two new topics, LeftSideAdvertising and RightSideAdvertising. I've then put the html straight in, in my case something like
<div class="block">
<div class="title">Advertising!</div>
HERE IS MY ADVERT!
<div class="clear"></div>
</div>