The amount of money spent by NHS Scotland on sending patients to the rest of the UK for treatment has risen by £3.3m in a year, official figures show.

Statistics from the country's health boards, obtained by the Scottish Liberal Democrats, show the organisation is now spending £15.2m a year on the practice.

A total of 625 Scottish patients were transferred out of the country for treatment at NHS Scotland's expense during the last financial year.

That figure is up from £11.9m, which was similarly spent on out-of-Scotland treatment in 2013/14 for only 427 patients.

During the past four years, the cost of the practice totalled £51.7m.

Lib Dem health spokesman Alex Cole-Hamilton said the rise must be explained by the Scottish Government.

He said: "It's important that patients in Scotland have access to the best possible care. If there is expertise elsewhere in the UK that they can benefit from then it is right that they can do so.

"However, we need to know whether the significant rise in patients being sent outside Scotland is a consequence of SNP ministers' failures.

"For example, the failure to plan the NHS workforce properly has led to huge numbers of long-term vacancies More than 250 consultant posts have been empty for six months or more."

In response to the figures, a Scottish Government spokesman said: "Spending on this very specialist care represents just 0.1% of the record £47.4bn investment in the NHS over the last four years, and a tiny proportion of the total number of procedures carried out in the NHS, which reached a record one million inpatient procedures last year.

"As complexity of healthcare increases and costs rise it is right that very specialised care for procedures such as lung transplants, is occasionally provided at specialist centres outwith Scotland to allow expertise to be concentrated and patients and families to be treated in quality settings."