There will be a by election in Barnhill on 3 May, following Judy Beckman's resignation as a councillor. Judy is a real loss to the Council, but she has decided that she wants to be nearer her family. The reason for leaving the election until 3 May is that having it on the same day as the GLA elections minimises cost. A Council by election costs between 20 and 25 thousand pounds. Holding it on the same day as another election removes much of the cost as the staff and polling stations would have to be available anyway.
The Liberal Democrats are rumopoured to be timing one election in Dollis Hill for late March, and another (in Dudden Hill) for July. This maximises the cost to the Council, but I assume they hope to do better on a lower turnout.