The legal limit for nicotine in the United Kingdom and across Europe is 20mg.
This has been deemed as the safest high concentration of nicotine that can be made available to the public whilst also allowing for heavy smokers to achieve a satisfactory switch.
In the United States and across many other parts of the world, there is not yet a limit on the concentration of nicotine in vape juices. As a result, higher strengths of nicotine are widely available in the US and can easily range from 30mg to 50mg.
In this context, whilst 25mg may not seem like a high amount in comparison to foreign territories, it is a level at which the risk of addiction is heavily compounded as nicotine is a highly addictive substance.