The number of patients leaving Britain and flying overseas for medical treatment has trebled as NHS waiting times reach a record high, a Telegraph investigation has revealed.

Government data shows the number of people going abroad for healthcare has increased from 48,000 in 2014 to almost 144,000 last year as the health service struggles to cope with demand.

Experts said lengthening waiting times for surgery - particularly hip, knee and cataract operations - and cutbacks to fertility treatment - were fuelling the rise.

NHS waiting times are now the longest they have been for almost a decade, with more than 409,000 people waiting more than 18 weeks for treatment - a rise from 34,000 in 2014.

Patient groups said the figures reflected badly on the NHS.

Joyce Robins, from Patient Concern, said: “It is a desperately sad state of affairs that people who have paid into the NHS all their lives are finding it is not there for them when they need it.

“These are essential operations, but thousands of people are being left in pain and misery - for every person who goes abroad there will be many more left suffering,” she said.

It comes amid a crackdown on “health tourism” within the UK. From Monday, hospital staff will be told to routinely ask patients for utility bills and bank statements in a bid to identify those from overseas who should be paying for NHS treatment.