Spokes keep breaking
The biggest cause of broken spokes, that I know of, is inadequate tension. When the spokes are tight enough they flex a little bit with every turn of the wheel as the spokes at the bottom of the wheel unload slightly and then tighten again as they move around to the top. Over time this bending back and forth weakens the spokes – usually at the bend where they pass through the hub – and eventually they break. The cure is to build the wheel with sufficient tension to prevent the flexing.

If the wheel is old (and since it is a 27" wheel, I'm inclined to think it is) then the damage may already be done – although it sounds like you've replaced close to half of the spokes by now.

All of the above assumes that you're riding a more-or-less normal bike in more-or-less a normal way…

To be much more help to you it would be helpful to have answers to the comments on the original question above. As a very quick and dirty check of tension you could grab a "handful of spokes" (a set of 4 from both sides of the wheel) where they cross and try squeezing them. It should be quite hard to get any flex out of them.