THREE former Edinburgh City Council leaders area among those due to give evidence as the inquiry into the city's trams project begins public hearings next week.

The probe, set up in 2014 by then First Minister Alex Salmond, is examining why the project went significantly over budget and was delivered years later than originally planned.

Among those due to appear are former city council leaders Donald Anderson, from 1999 to 2006, Ewan Aitken, between 2006 and 2007 and Jenny Dawe, leader from 2007 to 2012.

The inquiry will also hear from former transport convener Lesley Hinds, as well as the leader of the Scottish Conservatives on the council Iain Whyte and former Tory group leader Jeremy Balfour, now an MSP.

The following week will include evidence from Alan Coyle, former major projects manager at Edinburgh Council, and Nick Smith, former council solicitor and now head of legal services.

Six years in the making, the first trams started running in 2014 three years late, with the project eventually costing £776m, well above the earlier practical estimate of £545m.

The scandal prompted Mr Salmond to call the inquiry into what went wrong and the probe into the first part of the tram line, from Edinburgh Airport to York Place, is now reaching a new phase.

The inquiry is expected to hear that vast tracts of the city along the route were excavated, refilled and dug up again as utilities such as electricity and water pipes were rerouted and foundations laid during the construction of the system, with residents claiming some streets in the West End finally resembled "a war zone".

The former Lord Advocate and senior judge Lord Hardie is chairing the inquiry, said: "The oral evidence heard at these hearings will be used in conjunction with the wide range of evidence already gathered to inform my final recommendations.

"The inquiry team has already undertaken a substantial amount of activity including identifying, retrieving and reviewing more than six million documents and securing written statements from a significant number of witnesses.

"The hearings mark another important phase of this work."

The sessions for gathering oral evidence will take place on Tuesdays, Wednesdays and Thursdays and are expected to last for several months.

The oral evidence given at the hearings will supplement written statements from witnesses and documents recovered during the course of investigations by the inquiry team into why the Edinburgh Trams project "incurred delays, cost more than originally budgeted and delivered significantly less than planned".

The council is currently planning a £165m extension of the tram system along the original route from York Place to Newhaven. However, the final decision on whether to go ahead is not expected to be made until Autumn 2018.