I seem to remember having this conversation a few years back. I'll see if I can dig it up when I'm back in front of a laptop.
I always imagined it was the chimney of a kiln but there was a pottery in Williamson Road (where McDonalds and Sainsburys are) so having another one so close seems unlikely.
This is in fact the first and only completed wing of the North London Academy for Master Chimney Sweeps' Apprentices. The site by the New River was selected by the Guild of Master Sweeps as being "health enhancing and conducive to good work habits and cleanliness for the young apprentices." The interior comprises of segregated practice climbing chimeys, realistically constricted, for male and female aspirant sweeps. The gratings below at river level permit of combustion in wood-burning stoves, open coal fires and charcoal burners, thus replicating the myriad chimney conditions young chimney sweeps might expect to encounter on graduation to full apprenticeship. Unfortunately, this forward thinking Gove Academy, sponsored by the Guild of Master Chimney Sweeps, did not open until September 1874. While the 1870 Forster Education Act approved this scheme of Elementary Technical Training for 5-12 year olds in principle, Lord Shaftesbury's more ideologically driven Chimney Sweepers Act 1875 (superseding the more humane and enlightened Chimney Sweepers & Chimneys Regulation Act 1840) made the procuring of young apprentices ever more difficult for Guild members, with the result that the fruit of much progressive thinking on the furtherance of the useful arts and traditional crafts throughout the capital - in the very decade when great schemes of middle-class suburbanisation were being canvassed for the green fields of Harringay - withered within two semesters on the Hornsey vine.
I knew you'd know the answer (being around at the time of construction).
Here's the post I was thinking about - starting for the bottom of Page 1.
How intriguing! So am I right in thinking (from having mostly digested the other post but got a little lost along the way) that we still don't know for sure what it is?
Not for sure, but I've just added a new post to that thread.
So presumably we can look forward to its being reopened to provide Modern Apprenticeships for the work shy children of the poor...