More than half the self-storage space opened in the UK last year is sitting empty.

The occupancy level for space opened in 2014 was just 47%, rising to 70% for the average mature unit, according to research from Cushman & Wakefield in conjunction with the Self Storage Association.

The lowest occupancy rates were in the North, closely followed by the West Midlands and Wales. London, with 75% occupancy, was the highest in the country.

Openings of self-storage units in the UK plateaued with ten sites opening in 2014, a figure that has been static for three years and down from a high of 45 self-storage openings in 2002. The survey said expansion in the industry had been muted over the past four years owing to a lack of sites close to central London and continued difficulties in securing finance.

“While occupancy has remained somewhat low at 70%, the increase in the average rental rate by 7.1% shows that businesses are getting more for their storage space and not sacrificing revenue for occupancy,” said Rennie Schafer, chief executive of the Self Storage Association UK.

Average net billed room rates rose marginally last year from £19.61 in 2013 to £21 last year.