I've finally managed to get a good look at the actual tunnel; there's a foot bridge at the other end of the road which gives a view from about 200 metres away (according to Google Earth):
The yellow thing above the cutting is the mobile crane I've mentioned before.
My house is due south of the second of the cross-beams above the cutting. Artist's impression of what it will eventually be like - I don't know if this means that the cross-beams will be removed.
Unfortunately I couldn't go even an inch more to the right to take the photo, because the bridge has solid sides from that point onwards, rather than the steel grid I took this through.
The bridge behind the tunnel opening is the one that is going to be repaired - I hope that they will also be doing something about the potholes that keep appearing at its ends.
To make this clearer, the map showing the area is here
I took the pictures from the north end of the footbridge at the left, where it goes under trees. The tunnel opening is about 2/3rds of the way towards the bridge at the right.
According to the flyer we received about this, actual tunnelling will start in 2012.