New mayor of London Sadiq Khan has begun an investigation into the actions of predecessor Boris Johnson when procuring the planned the "Garden Bridge". Khan, who has only been mayor for 10 days, is said to be looking into why the designer of the bridge was apparently chosen before an official tendering process was completed, and why it was claimed by Johnson the bridge would only be funded by private finance only to later guarantee public investment.

The concept for the 367m pedestrian bridge, between Temple and South Bank, came from an idea by actress Joanna Lumley, a childhood friend of Boris Johnson. The bridge, due to begin construction later in 2016, will feature plants, trees and walkways and provide the eighth footbridge between north and south London for pedestrians and commuters.

A spokesman for Khan says the new mayor wants to know why public money has been pledged when Johnson had said it would be financed entirely by the private sector.

Speaking on LBC radio about the £30m ($43.08m) grant from Transport for London (TfL) in 2015 Johnson was asked if any more public money would be used.

He replied: "No, the maintenance costs will not be borne by the public sector and I've also made that clear."

However, Johnson later said the Greater London Authority (GLA) would act as a guarantor for the bridge's upkeep if the trust set up to raise funds – the Garden Bridge Trust – fails.

It is now up to Khan to sign the guarantee, and it is unclear if he will do that ahead of the investigation being concluded. However, the new mayor is said to be positive about the project. "The mayor supports construction of the garden bridge, but expressed concerns during his election campaign about the way the procurement process was carried out," said his spokesman.

In addition to the £30m grant from TFL, the Treasury is to pay £30m towards the bridge's construction costs. Also, £3.5m of public funds will be put towards the bridge's running cost each year.

It also emerged that Johnson held a meeting with architect Thomas Heatherwick on 1 February 2013, before Heatherwick was invited to tender for the project. Johnson failed to mention the meeting in his report to the GLA. There is no suggestion Heatherwick has done anything wrong.

The 'garden bridge' will be built on the top of Temple underground station. The public green park next to the station will be redeveloped into a commercial building as part of project.

In November 2015, the Guardian reported that planning documents for the bridge filed with Lambeth council detailed that people's mobile phones would be tracked while they were on the bridge, it would feature a video surveillance system and civilians patrolling the bridge would be granted limited police powers. In addition, all exercise, except jogging, would be banned, in addition to playing musical instruments, forming a "gathering", giving a speech, scattering ashes, releasing balloons and flying kites