The findings follow a survey of 5,863 smokers who had attempted to stop smoking without the aid of prescription medication or professional support.
Of those using e-cigarettes, a fifth reported having quit "real" cigarettes at the time the study was carried out.
The research, published in the journal Addiction, suggests that e-cigarettes could play a positive role in reducing smoking rates, say experts.
Study leader Professor Robert West, from University College London, said: "E-cigarettes could substantially improve public health because of their widespread appeal and the huge health gains associated with stopping smoking. But the strongest evidence remains for use of the NHS stop-smoking services."