The Finance Secretary has been warned over the possible "unintended consequences" of an extra charge for buy-to-let properties and second homes.

MSPs unanimously backed the general principle of a new supplement of 3% of the total price of properties over £40,000 but called on John Swinney to ensure that the legislation, if passed, is carefully monitored.

During an initial debate at Holyrood, Mr Swinney said he was prepared to bring forward several amendments to the Land and Buildings Transactions Tax (Amendment) (Scotland) Bill, including a relief when six properties or more are bought together.

This was among the recommendations of the Scottish Parliament's Finance Committee, which heard fears the policy could deter investment.

The committee also called for a grace period to allow time for a previous property to be sold and additional reliefs for registered social landlords, local authorities and student accommodation.

Mr Swinney said the aim of the Bill was to maximise the opportunities for first-time buyers to get a foot on the property ladder in Scotland.

He told MSPs: "I certainly recognise the need to balance support for home ownership and first-time buyers without discouraging significant and beneficial investment in residential property for rent.

"I hope that the specific relief that I have set out in relation to the bulk purchase of properties gives some further clarity to the market place and can enable commitments to be made with the assurance I have given."

The Finance Secretary said the issue of additional reliefs would be kept under review as more data was collected on the impact of the supplement, which will be paid on top of Scotland's stamp duty replacement.

He said he was not convinced about the need for a grace period but remained open to considering it in the future.

Mr Swinney's move followed a similar decision by Chancellor George Osborne in November's UK Autumn Statement.

Labour MSP Jackie Baillie pointed out that the House of Commons Treasury Committee was "not enamoured at all" with the supplement south of the border and questioned what would happen if the move was delayed in the rest of the UK.

She said: "There is a very strong suggestion coming from them there should be no rush to implementation because of the complexity and because of the possibility of unintended consequences.

"They also feel it would actually be detrimental to the buy-to-let property market and recognise the importance of this sector for labour mobility."

Ms Baillie added: "There are unintended consequences that we should be alive to and not simply just look narrowly at the principle and nothing else."

Conservative MSP Gavin Brown said: "It certainly appears clearly to me that both north and south of the border this measure is far more complex than first appeared when it was announced in the Autumn Statement."

He added: "It's my view that the risk of inaction is greater than the risk of unintended consequences flowing from legislative action.

"That said, there are clearly significant issues to resolve and I think the Government would accept that."