Image caption Office development in Belfast has slowed since the 2008 property market crash

Rents for premium office space in Belfast city centre have risen by 19%, but experts say still not enough to generate a boom in developments.

Rents for grade A offices have risen to £15.50-per-sq ft over the past year, according to commercial agents.

But they are still well below the UK average of £24.

It is claimed that the prospect of a relatively low financial return is acting as a barrier to substantial build projects.

In March, an Invest NI report said there is a shortage of grade A space office in Belfast.

Grade A offices are classed as new or refurbished buildings, in prime locations, with open-plan layouts.

Ian Duddy of Colliers International in Belfast said: "The shortage of grade A space in Belfast has led a number of major occupiers to develop their own headquarter buildings.

"Further rental growth in the grade A market is necessary to encourage new development in the city."

Office development has slowed since the 2008 property market crash.

Loans of public money could soon be made available to property developers to help them build offices, after a recent report for Invest NI described supply as "extremely limited".

Invest is exploring whether to advance loans as "a short-term intervention".