The SNP government has sidestepped its first Holyrood defeat by accepting an amendment by opposition parties that it should not "arbitrarily" scrap projects such as the Edinburgh airport rail link and trams scheme.

Avoiding a vote today just puts off D-day for a month, when the SNP will have to come forward with firm, evidence-based proposals on whether to abandon or downgrade either project.

But the tactical withdrawal in the face of certain defeat was the first insight into the cat-and-mouse game of minority government which will be played out over the next session.

Finance Secretary John Swinney said last night: "The government will not decide any matter on an arbitrary basis, and therefore we have no difficulty in supporting the amendment. A decision on Earl the Edinburgh airport rail link and trams can only be taken when the government is in a position to present full financial information to the parliament in a considered fashion. That is the job of government."

Ambitious plans for a new rail terminal under Edinburgh Airport, costing £650m, and a tram service through the west of the city and on to Leith, costing more than £500m, were agreed after much debate by the last parliament.

But the SNP manifesto committed the party to scrap both schemes as too costly, saying the money should be spent elsewhere on improving rail links across the country.

There was an angry reaction in the chamber yesterday from former Liberal Democrat transport minister Tavish Scott to SNP suggestions that the costings of the projects were "out of control".

The LibDems and Tories then agreed to back a Labour amendment to today's motion on removing Forth and Tay road bridge tolls adding a warning to ministers that projects already approved by parliament "should not be arbitrarily delayed or cancelled".

By accepting that amendment, the SNP avoid suffering its first defeat but there will still be a vote as the two Greens will want to register their opposition to the ending of bridge tolls.

Greens are in favour of trams but hostile to the Earl scheme, pointing out that a report last year said the latter undermined the business case of the former. Edinburgh civil and business leaders are fighting to save the trams project.

Yesterday began with the executive firmly rebutting any suggestion that there was any link between the proposed abandonment of two schemes and the long-term aspiration to dual the A9 between Perth and Inverness.

An executive spokesman said: "This is a false comparison. There is no connection between plans for public transport investment in Edinburgh and other long-term plans for transport improvements, as the projects are funded from different budgets and operate to different timescales."

The Earl scheme is viewed with particular scepticism in its present form as it involves rerouting both the Fife rail line and the Glasgow/Stirling line through tunnels under the main runway to create a new station there. Planners may now have to dust down less ambitious versions of the airport rail link.

The SNP also have "deep misgivings" about the Edinburgh trams project but as this is further advanced and would also serve the airport it is believed there is more chance of a change of heart on that.

A comment by Transport Minister Stewart Stevenson that the costs on these schemes was "out of control" prompted Mr Scott to say: "I do hope the government can absolutely demonstrate what advice Mr Stevenson got to make that remark in public.

"It's no good inventing a justification in order to make a political decision, and that's what I fear they are doing."

Specific concerns about the costings of the Earl and tram schemes will be brought to parliament within the next four weeks along with a recommended course of action.