Google and Apple are on their way to produce aerial maps so detailed they can show up objects just four inches wide, according to report published by Daily Mail. Google will use its spy planes to help create 3D maps with much more detail than its satellite-derived Google Earth images.

The report said that Google admits it has already sent planes over cities while Apple has acquired a firm using spy-in-the-sky technology that has been tested on at least 20 locations, including London.

Apple’s military-grade cameras are understood to be so powerful they could potentially see into homes through skylights and windows. The technology is similar to that used by intelligence agencies in identifying terrorist targets in Afghanistan.

"Since 2006, we’ve had textured 3D buildings in Google Earth, and we are excited to announce that we will begin adding 3D models to entire metropolitan areas to Google Earth on mobile devices”, Google said in a statement last week

"This is possible thanks to a combination of our new imagery rendering techniques and computer vision that let us automatically create 3D cityscapes, complete with buildings, terrain and even landscaping, from 45-degree aerial imagery. By the end of the year we aim to have 3D coverage for metropolitan areas with a combined population of 300 million people."

According to Telegraph.co.uk, Apple has recruited a private fleet of aeroplanes equipped with military standard cameras to produce 3D maps so accurate they could film people in their homes through skylights, according to reports.

The US software giant is expected to announce this week a new "Maps" programme for iPhones and iPads allowing users to view images previously out of reach to anyone but the intelligence services.

Producing images of streets, homes and gardens so clear they will show objects just 4in across and display the sides of buildings as well as their roofs, the product is aimed as a direct challenge to Google Maps.

The technology is understood to have already been tested in 20 cities across the world including London following Apple's acquisition of C3 Technologies, a Swedish 3D mapping business, last year.