It is believed that David, 38 and Victoria, 39 are sparing no expense on the seven-bedroom house, which is apparently near Kensington Palace, where Prince William and Kate Middleton live, reported Daily Mirror.
"Security is a concern and the new house has a soundproof panic room," a source said.
The new home will have five bathrooms, an indoor cinema, library, underground car park and staffed massage rooms.
"After months of searching they have found their dream city home. Their offer should get accepted any day now. It is in a perfect, quiet location with discreet, well-to-do neighbours. David and Victoria want everything perfect. It will be unique," the source added.