Plans to roll out a new benefit should be halted in Scotland to allow for a "meaningful discussion" to take place about devolving welfare powers to Holyrood, the Deputy First Minister has said.

Nicola Sturgeon, who is expected to become Scotland's new first minister next month, has written to David Cameron to demand the introduction of Universal Credit be put on hold north of the border.

It comes in the wake of the vow made by Mr Cameron, Ed Miliband and Nick Clegg in the run-up to the independence referendum to devolve powers over welfare to Scotland if the country remained in the UK.

Ms Sturgeon said it was hard to see how the "main proposal" from the Westminster parties to hand power over housing benefit to Holyrood could proceed if the UK Government presses ahead with plans to bring in Universal Credit.

The reform brings together six different benefits and tax credits into one payment and is currently operating in Inverness as well as some parts of England.

Work and Pensions Secretary Iain Duncan Smith told the Conservative Party conference this week that he was going to finish what he started with Universal Credit despite the scheme so far being blighted by cost overruns and delays.

Mr Duncan Smith said: ''I can announce that we are going to accelerate the delivery of Universal Credit from the New Year, bringing forward the national roll-out through 2015/16 to every single community across Great Britain."

But Ms Sturgeon said: "It is hard to see how this is in any way consistent with a good faith approach to the process of agreeing more powers for the Scottish Parliament."

She argued the roll-out of the new benefit should be put on hold in Scotland until after talks about further devolution have taken place.

"There is a widespread consensus that the Westminster parties' proposals on the devolution of welfare powers are far too timid and that the Scottish Parliament needs substantial control of the welfare system to help people into work and tackle the growing scandal of poverty in Scotland," Ms Sturgeon said.

"However, it is hard to see how even the limited welfare proposal of the main Westminster parties - to devolve control of housing benefit - can be delivered if the UK Government presses ahead with Universal Credit.

"Universal Credit effectively abolishes housing benefit. It is not clear to me how we can have a meaningful discussion about devolving a welfare policy that is already in the process of being abolished.

"I have, therefore, written to the Prime Minister today asking that the roll-out of Universal Credit - which in any event is already significantly delayed and discredited - is halted in Scotland.

"It is essential that the Westminster parties respect the process of agreeing more powers in actions as well as words."

She added: "There is already concern that Westminster wants to backslide on the promises made before the referendum.

"David Cameron's statement linking more powers for Scotland to English votes for English laws, Ruth Davidson's attempt to rule out devo-max before the Smith Commission even gets to work and Gordon Brown's call for people to sign a petition to demand change that he previously said was a done deal have done nothing to build confidence amongst the Scottish people that the pre-referendum 'vow' will be honoured.

"To press ahead with a discredited policy that will undermine the substance of future discussions would only heighten that concern.

"I have said clearly that the Scottish Government is entering discussions on more powers in good faith.

"I am calling on the UK Government to demonstrate in actions - not just in words - that it is doing likewise."

A UK Government spokesman said: "UK Government business continues as planned and we will not pre-judge the outcome of the Smith Commission.

"Further devolution proposals will be set out by the end of November following an invitation for input by all five of Scotland's political parties."