Accountancy body warns over new tax powers for Scotland
Devolving further tax powers to Scotland would be "more complex than many might anticipate", Scotland's accountancy body has said.
The Institute of Chartered Accountants of Scotland (ICAS) highlighted factors such as tax competition within the UK and the need to reduce tax avoidance.
A commission is considering proposals for more powers for Scotland after voters rejected independence.
ICAS also asked whether the Scottish population would accept the changes.
Property and landfill taxes have already been devolved to Scotland and more tax powers are expected.
In his draft budget for 2015-16, Finance Secretary John Swinney set the rates of the Land and Buildings Transaction Tax, which replaces Stamp Duty in Scotland, and the new Landfill Tax.
The tax powers were conferred on the Scottish Parliament by the Scotland Act 2012, along with the power to set a Scottish rate of income tax.
Ahead of the 18 September referendum, the main pro-Union parties set out individual proposals to deliver more powers for the Scottish Parliament.
After the vote, Prime Minister David Cameron announced the establishment of a commission, chaired by Lord Smith of Kelvin, to consider these proposals and those of the pro-independence SNP and Scottish Green Party.
All five parties have proposed further tax powers, ranging from Labour's plan for Scotland to raise 40% of its budget through increased tax-varying powers, to the SNP's proposal that all tax revenues should be retained in Scotland unless there is a "specific reason" for any to remain reserved to Westminster.
ICAS, which produced a report before the referendum on the tax implications of either further devolution or independence, said it maintained "an apolitical stance".
The professional body for accountants said: "The design of any new taxes should be based on sound principles, such as simplicity, neutrality, stability and flexibility."
It added: "The design of a tax system involves many trade-offs and compromises, and these need to be recognised, for example there is often a trade-off between simplicity and fairness and between the tax revenue required for public expenditure and the level of taxes set.
"The key risks with any changed tax system are whether the desired level of revenue will be raised and whether the population will accept the changes, especially to tax rates."
According to ICAS, the risks included the possibility of taxpayers "falling through the cracks" during a transfer to new taxes, and that differing tax rates might encourage people to "move across the border or 'game the system'".
And setting up and administering new taxes "would require a considerable amount of resources", the body argued.
Lead researcher Prof Jane Frecknall-Hughes said: "The issues that would need to be considered in relation to taxation under further devolution are wide-ranging and more complex than many might anticipate.
"Any substantial changes would require very considerable and careful thought."
The Smith Commission is expected to reach agreement on the way forward by 30 November.
Lord Smith has said that reaching agreement "will not be easy" but has told the parties: "Scotland is expecting us to arrive at consensus."