Transport authorities under Gladys Berejiklian sought second and third rounds of probity advice after first being told not to extend a lease over RailCorp land in Sydney's inner west – an extension that is likely to cost taxpayers tens of millions of dollars.

The Premier faced persistent questioning in Parliament last week about decisions made while she was transport minister that have complicated the construction of the WestConnex motorway.

Ms Berejiklian denied knowledge of the 2012 decision to extend a lease held by a company owned by business figures Shane Barr and Robby Ingham over a plot of land at Leichhardt.

The decision to extend that lease, which was due to expire next year, means taxpayers face a bill in the tens of millions of dollars to compensate the leaseholders and sub-leaseholders of the land if, as is likely, the site is resumed for WestConnex tunnelling.