I moved a 10 inch high, ornamental concrete house, with holes for windows, from the border onto the lawn in early May 2010. On the ground, where the little house had stood was a completed Tits' nest containing two eggs. Both eggs were cold, and so I assumed the nest had been deserted because of my gardening activities.  Four days later, with the house still sitting on the lawn where I had left it, I picked it up to move it.  Underneath - a new, half-built nest!  I picked up the half-built nest, placed it back in the border in a totally different position from its original location ( a plant now occupied that spot!), positioned the house over the top of it and withdrew, never thinking that the bird would resume nest building.  About a week later, though, Great Tits were seen going in and out of the house, and at the time of writing( 7 June), are busy feeding a brood. Persistent little blighters - thank goodness!Great Tits