The British Geological Society have produced a digital map under the heading 'OpenGeoscience' so you can search on your postcode.

The map can give an indication as to the type of rocks that lie buried below. It is meant for private study, research and educational activities. It might prove useful as a guide to the subsoil you could encounter should you be thinking of building an extension, but please be aware that it is not 100% accurate and must not be used for commercial purposes. For more precise subsoil information have a chat with your building control officer or contact organisations such as the British Geological Society to commission a report.

Please remember that the use of any information available from OpenGeoscience must not be for direct or indirect commercial gain. Further information is available at following this link.