Ambitious plans to renovate the parliament complex in The Hague have been thrown into doubt once more after junior interior minister Raymond Knops revealed the project may have to be delayed by a year.

Knops said the need for up-to-date security measures and the recent Council of State judgment requiring tighter rules to compensate nitrogen emissions were among the reasons for the likely delay.

The government has also allocated more money for parliamentary staff in response to a report calling for better support for MPs to scrutinise its work. The plans will need to be redrawn to create space for the extra personnel, Knops said.

The minister also said that the budget would have to be increased by an estimated €16 million to reflect 2019 prices.

The €475 million overhaul is due to start in September 2020 and last five and a half years, but is already proving controversial. Some MPs are unhappy about the time and cost involved and say it should be restricted to a maintenance upgrade.

Knops said it was proving challenging to install IT and audio-visual equipment in the Tweede Kamer’s interim home in the foreign affairs ministry’s builiding on Bezuidenhoutseweg. ‘Margins in the construction sector are as tight as ever, which means long delivery times for parts and limited flexibility in the market,’ he wrote in a letter to parliament.

The current lower house building was opened in 1992 but has only undergone minor repair and maintenance work since then. The upper house and council of state are moving in to the former High Court building on Lange Voorhout while the renovation is carried out, while the prime minister’s department (Algemene Zaken) will move into the Catshuis.