Scotland will have the power to change its voting system and alter the length of its parliaments, under devolution proposals to be unveiled this week.

It is understood that the Smith Commission report, which is expected to be published on Thursday, will recommend that the Scottish Parliament in Holyrood, Edinburgh, is given control of its own electoral system.

David Cameron asked Lord Smith of Kelvin, a former governor of the BBC, to look into the granting of more powers to Scotland, following the close referendum vote in September. The major political parties in Westminster pledged a significant, but vaguely defined, package of devolution in a successful effort to see off a late surge in support for independence.

Holyrood was set up in 1999 with four-year, fixed-term parliaments. However, it was the coalition government in Westminster that decided to delay the 2015 vote by a year so that Scottish elections did not clash with the general election, a move criticised by the Scottish National Party.

Under Lord Smith's proposals, such interference could not happen again. Similarly, should future Scottish governments choose to ditch the semi-proportional added member system used north of the border, they could do so. A senior Scottish politician said Holyrood would have "control of its own elections, select a different period of time [between elections] and choose whatever system it wants, such as the Single Transferable Vote".

The source added that a "substantial" set of tax-raising and welfare powers would be handed to Holyrood. However, the SNP is expected to fight hard on the tax recommendations if these offer anything less than full autonomy for Holyrood on all levies ﻿and responsibility for all domestic expenditure that is not shared with the rest of the UK.

Nicola Sturgeon replaced Alex Salmond as Scotland's first minister last week, making headlines by unveiling a gender-balanced, 10-person cabinet. Yesterday, Ms Sturgeon addressed a sell-out audience of 12,000 at the SSE Hydro in Glasgow. In the event of a hung Parliament in Westminster, she said, the price of coalition with Labour would be no more nuclear weapons, but the SNP "would never act to put the Tories in power".