"Perhaps they've not made it explicit that they're not prepared to do so but, implicitly, they've made that clear by closing down issues of consideration around the Scotland Act.
"I think the questions on further tax devolution are somewhat embedded in the debate on the referendum."
He was asked by committee convener Kenneth Gibson if any further taxes are being considered for devolution.
The Act provides for the income tax rate in Scotland to be reduced by 10%, with the Scottish Parliament then responsible to bring it back up or make variations. The power is expected to come into force in April 2016, just before the next Holyrood election. Borrowing limits will be increased, giving ministers the power to raise up to £2.2 billion to fund capital expenditure from April 2015.
The independence referendum is expected to be held in 2014, potentially superseding the Act's provisions.