Is it possible to extend the roof over to which I presume is an adjoining property? A breeze-block wall is fairly well absorbent thing - as you now know. Sadly, if you seal over the interior, you shall be asking for trouble should the blocks become waterlogged and then freeze...! The protective covering on the outside is by far the best for this reason... Anyhoo, on the inside, you can add render with a healthy dose of waterproofer in it, which is the cheapest option. The expensive, but FAR superior option is to apply a 'tanking slurry' The one I use is Vandex, but there are many others to choose from. Good luck