No, it is illegal to ride a motorcycle on public roads in the UK without a valid license. In the UK, you must have a valid motorcycle license to legally operate a motorcycle. The type of license required depends on the size and power of the motorcycle you wish to ride. There are different categories of licenses, such as the AM license for mopeds, the A1 license for motorcycles up to 125cc, the A2 license for motorcycles up to 35kW, and the full category A license for unrestricted motorcycles. It is important to obtain the appropriate license and comply with the legal requirements to ensure your safety and the safety of others on the road.