http://www.stagecoachbus.com/serviceupda...px?Id=6712
It seems to have something to do with the Better Bus Improvement programme on Borough Road. On the 24th, buses will essentially be doing almost a full lap around Mowbray Park, including a loop around the Burdon Road/Stockton Road/Park Road gyratory. I've just done a quick measure on Google Earth, and the diversionary route is a whole mile longer than the usual route and plus all the extra traffic light junctions to pass too - so expect delays!
Went past Borough Road on the 10 on Thursday - there is a bus shelter at the west-bound stop opposite William Jameson but it's not in use yet.