The new Cabinet Secretary for Planning, Alex Neil, has pledged to investigate the cause of a slowdown in the planning system that prompted a scathing broadside from a leading industry expert last week.

Allan Lundmark, who was head of planning at housebuilders' group Homes for Scotland for 13 years, attacked the Scottish planning system in a retirement statement, saying a "depressing" six-week increase in planning decision times in the last quarter are evidence of "a system which falls far short of the standards of customer service, speed and efficiency that Scotland needs if we are to build more homes and stimulate economic growth".

He added: "It is hugely disappointing that after so many years of positive industry engagement and supposed planning reform, we are still … fighting for a system which encourages and facilitates housing investment rather than one which frustrates and delays it."

A spokesman for Neil told the Sunday Herald the minister had "asked officials to investigate" the fact that "timescales for major housing applications decided in the last quarter did increase", and pledged to "come back to you in the new year as soon as possible" with the results.

The minister also stressed that the recent statistics "show major ­developments are being processed more quickly than last year.

Neill added that between July and September, the highest ­quarterly number of local housing developments was processed, and more quickly than ever before".

Craig McLaren of the Royal Town Planning Institute, which represents the planning profession, blamed lack of central and local government investment in the system.

He said: "Planning can't be seen as the Cinderella service of local government - it is vital it is resourced to help deliver more homes and stimulate economic growth."

Monica Lennon, a chartered town planner and Labour councillor for South Lanarkshire, said: "Investment in a proactive planning system is key to delivering the homes, infrastructure is desperately needed across the country and collaborative approaches are needed more than ever."