From the OS:
"Basic work has already started at the Staplewood site, with temporary buildings and accommodation already in place for the first team squad. Now that planning permission has been granted, the next stage is to immediately begin constructing additional temporary accommodation before demolishing the existing buildings in the coming months, with work set to start on the new structure around July. A period of nine to twelve months has been set aside for the construction process."
If the temporary accomodation doesn't spring up by June or so, then you can worry.