Joined: 18 Jun. 2015
For anybody interested. I contacted Parliament direct and they responded with a pretty thorough response.
I'll paste it below:
I have been going through some of the information on the parliament website and some of the books and material that we hold. We have information on the architecture, however most of the focus is on the main towers, the Victoria Tower, Elizabeth Tower and Central Tower. I have been able to find very little about the towers/spires you point to on your photograph. From what I have been able to find through research and conversation is that, like Central Tower, they acted as chimneys/ventilation openings, although I haven’t been able to find particular names for them. As regards the colour, it could be a combination of the cast iron in the design and possibly the effects of London pollution throughout Victorian times and simply be dirty/discoloured. Again I haven’t found anything definitive either way.
The one you originally ask about, on the riverside in the centre of the building, stands above Lower Waiting Hall. From Lower Waiting Hall you can take stairs up to Upper Waiting Hall and from there access the Committee Corridor and the Committee rooms which run along the length of the building. I cannot find if the tower simply marks the Lower Waiting Hall or if its original Victorian function was related to ventilation on the floor or as chimney for the committee rooms. Of the other towers you point to, the one closest to Big Ben and the Elizabeth Tower end stands above the Speaker’s Chair end of the House of Commons Chamber. The tower at the far end of the building near the Victoria Tower, stands above the House of Lords Library. The final tower you point to, just to the south of Central Tower (above Central Lobby), stands above the end of the House of Lords Chamber, near Peers Lobby. Again unfortunately I haven’t been able to find particular names and if they had any practical function or were simply part of the design of the building.
There is information on the Architecture of the Palace on the parliament website via this link, although it does not have any detail on these ‘lesser towers’. There is also a page here on further information and references which I have not been able to look into however if you have access to a library you may be able to find some of them. I did also find a page on a website on Victorian technologies which describes how ventilation was built into the building. While this is not an official parliamentary page you may find the information of use, and you can access the page via this link.
I hope this is helpful and goes some way to answering your questions.