Yes, Twin Flat with Earth cable can be used outdoors, but with certain considerations and precautions. This type of cable is typically designed for indoor use, so when using it outdoors, it is crucial to ensure it is adequately protected from environmental factors such as moisture, UV radiation, and physical damage. 
To use Twin Flat with Earth cable outdoors safely, it should be installed in a protective conduit or trunking that is rated for outdoor use. This will shield the cable from direct exposure to sunlight, rain, and other weather conditions that could degrade the insulation over time. Additionally, the conduit should be sealed properly to prevent water ingress, which can lead to electrical faults or corrosion.
The cable should also be rated for the specific environmental conditions it will encounter, such as temperature extremes. If the cable is not inherently UV-resistant, the protective conduit will help mitigate the risk of UV damage. 
Furthermore, local electrical codes and regulations should be consulted to ensure compliance with safety standards for outdoor electrical installations. In some regions, specific types of cables are mandated for outdoor use, and using a Twin Flat with Earth cable might not meet these requirements without additional protective measures.
In summary, while Twin Flat with Earth cable can be used outdoors, it requires proper protection and installation to ensure safety and longevity. Always consult local regulations and consider using cables specifically designed for outdoor use if possible.