I had no idea that trains couldn’t use both centre platforms to go East to West. What exactly was the point of that?!
Been that way since the early 1900’s. The ability to reverse one train in either direction whilst another could be routed round was generous enough given how hemmed in the site still is. Today’s pair of trailing crossovers probably was down to cost given that No. 25 road was abolished.
I trained at Whitechapel cabin, nearly 45 years ago, and a train could go forward from either platform 1 or 2 into the tunnel and reverse under a shunt signal into platform 3 or 4.
Another thing you could do at Whitechapel was berth a 6 car C stock further down 21 road (on the diagram above) and still use platform 1 to reverse a train. A draw up (permissive) signal protected the train berthed. It usually only happened if there was a defective C stock. It was operating policy not to reverse C stocks in platform 2 unless unavoidable, ie two in a row.
25 road was rarely used because the passengers would have to be detrained at Stepney Green or another shunt move into the eastbound tunnel and back.