A mystery American donor has given £1m to a historic steam railway in the Scottish Highlands.

Strathspey Railway said the US-based benefactor, who wishes to remain anonymous, was impressed by the railway after a visit years ago.

The volunteer-run company, based in Aviemore, said it the “exceptionally generous” gift would help cover costs for operating and refurbishing its locomotives.

The heritage railway has been a location in several TV programmes, including three series of The Traitors, which is filmed at Ardross Castle near Alness.

The company’s board said it was taking financial advice to ensure the donation is invested effectively for the short and long term.

A spokesperson said: “This exceptionally generous – and unexpected donation – will allow the railway to rebuild its financial reserves whilst being able to invest in a number of projects which will underpin the sustainability of the railway.”

Strathspey Railway operates a 10-mile (16km) route between Aviemore and Broomhill, via Boat of Garten.

The railway has also appeared on screen in BBC drama Monarch of the Glen and ITV’s Doctor Findlay.