Foreign patients who seek private treatment in the UK are a lucrative source of income for the NHS, research has found.

International patients can generate a third of the income trusts earn from private patients - despite the fact that most hospitals only treat a relatively small number, according to researchers from the London School of Hygiene and Tropical Medicine and the University of York.

Freedom of information requests to 28 hospitals found that a small number of foreign private-paying patients were responsible for 35 per cent of private income in these trusts.

“This indicates that private foreign patients may be more lucrative than UK patients treated privately within the NHS,” the authors wrote in the BMJ.

The researchers added that the UK is a “net exporter” of patients.

“More UK residents currently travel abroad for treatment than international patients travel to the UK to access treatment here (in the NHS and privately),” the authors said.

“Depending on the procedure undertaken, patients who travel abroad may also save the UK resources.”