Moves are under way to challenge plans for the new Edinburgh tram extension to Leith and Newhaven.

Proposals from inside and outwith Edinburgh City Council are expected to be made against a preferred £145 million two-mile addition to the current system.

It comes as historian and former MSP Professor Christopher Harvie raises concerns in The Herald today over the cost of this part of the controversial project compared to other European and UK tram systems.

The council said the proposal only came after detailed investigation and is still under close scrutiny by its legal team.

Mr Harvey, SNP MSP between 2007 and 2011 and a former president of the Scottish Association for Public Transport for nine years, said the cost per kilometre is up to double that of similar projects.

He also claimed paying for that move could restrict the potential extension of the tram system to other parts of the Scottish capital and possible future rail-tram links.

Mr Harvey, Professor of British Studies at Tuebingen in Germany, said the bill for the extension "seems unreasonably high when Nottingham's tram system cost £20m per kilometre".

He said: "If Edinburgh already has the rails and up to ten spare trams, and has (painfully) done much of the Leith foundation work, why this expense?

"Success in whittling-down inflated tenders and spreading the geld will open up new long-term perspectives.

"A rationally-costed Leith line could help set Edinburgh up for a Bridges-Infirmary/Shawfair to South Suburban tram: relieving Princes Street and extending into Lothian."

Cameron Rose, Edinburgh Conservative group leader, said there will be challenges to the existing plan and criticised the council for not waiting until the outcome of the inquiry is completed into what went wrong with the initial tram project.

Lord Hardie is chairing the ongoing probe, called for by former First Minister Alex Salmond, into the trams project. which f

Trams finally started running in May 2014 after six years of disruption. The project cost £776m, more than the original £545m, and arrived three years late.

Mr Cameron said: “It does appear to make sense to extend the tram system."

However, he added: "At the kind of price of the proposal that has been put in front us would we not be better to wait for tram inquiry?"

He said there would be further pressures on the project with additional cuts to the council budget now expected from Holyrood.

The current plan is still under scrutiny and Mr Cameron said it would be opposed at that cost.

He said: “They have decided to go ahead in principle but have left options to pull out in the coming months.”

The council said the new development would act as an economic stimulus for Leith and Newhaven and the wider, stalled regeneration of the waterfront and docklands.

It was claimed lessons had been learned from the previous fiasco.

A nine month period of site investigation, procurement and other preparation comes next, and then a report will recommend how best to proceed with the development.

Andrew Burns, council leader, said the council had been able to "find a way forward for the project, which would deliver a range of key benefits in terms of economic growth, greater accessibility and the environment for Leith and the city as a whole".

He also said: "It is now our intention to ensure complete clarity before taking the next step, taking into account the needs of the city’s taxpayers.”