Alun Cairns Welsh Secretary after Stephen Crabb's promotion

Alun Cairns has taken over from Stephen Crabb who has been promoted

Alun Cairns has become the new Welsh secretary after Stephen Crabb was made work and pensions secretary in the wake of Iain Duncan Smith's resignation.

Vale of Glamorgan MP Mr Cairns steps up from his role as under secretary of state at the Wales Office which has been filled by Aberconwy MP Guto Bebb.

Prime Minister David Cameron made the announcement on Saturday.

Mr Duncan Smith quit on Friday over the latest planned cuts to disability benefits announced in the Budget.

Mr Cairns told BBC Wales: "There is no better role for Wales than sitting around the cabinet, making sure that Wales' voice is heard loud and clear and also in shaping UK government policy developed to Wales' benefit."

Mr Cairns said he wanted to see Cardiff's Capital Region city deal to be as successful as the last biggest infrastructure project, the regeneration of Cardiff Bay, and he wants to push forward similar projects for north Wales and Swansea.

"This has been an extraordinary week for Wales with a city deal for Cardiff Capital Region, the doors being opened for a north Wales growth deal and negotiations for a Swansea Bay city deal.

"The Severn tolls announcement demonstrates that Wales is open for business and I am determined to keep this momentum going and deliver on these projects."

Who is Alun Cairns?

• 45-years-old

• Conservative MP for Vale of Glamorgan since 2010

• Became a junior minister in the Wales Office in July 2014

• Served as a Tory AM for South Wales West from 1999 to 2011

• Has worked for Lloyd's Bank

• Was the fastest MP to complete the London Marathon last year

As the new Welsh secretary, he will take charge of steering the next stage of Welsh devolution into law.

Up until Saturday Mr Crabb had responsibility for the Wales Bill, a new law which significantly changes how the assembly works and gives it new powers. However, it has proved controversial.

The draft bill led to claims from First Minister Carwyn Jones, Presiding Officer Rosemary Butler and others that it actually reduces powers in the assembly.

It was criticised from all corners of the assembly, including Welsh Conservative AMs, and Mr Crabb promised changes in response.

He also delayed the publication of the final form of the bill to go before MPs until at least May. Its publication will now be the responsibility of Mr Cairns.

Mr Crabb said: "I was delighted to see Alun Cairns appointed as my successor as Welsh secretary. I think he'll do a fantastic job.

"I think the Wales Bill - with the changes I announced in recent weeks - is in good shape to take forward to Parliament now but obviously it will be for the new secretary of state for Wales to lead that through in the manner in which he sees fit."

Welsh Conservatives leader Andrew RT Davies said Mr Crabb's appointment was "just rewards" and welcomed Mr Cairns as a "tireless and effective voice for Wales".

Analysis by Nick Servini, BBC Wales political editor

This is a major career development for both men.

But Stephen Crabb has an enormously difficult job of steering through highly controversial welfare changes, given the man formerly doing the job described some of those changes as "indefensible".

For the new Welsh secretary, his complete focus is infrastructure. Alun Cairns thinks the Wales Office job is much more of a challenge because of George Osborne's preference of delivering infrastructure projects through city deals.

In Wales, this has to be delivered through devolution, which makes it more complicated than in the north of England.

Mr Crabb's marked change in tone from his own predecessors - his more consensual attitude to Cardiff Bay - was welcomed across the assembly.

Mr Cairns very much wants to be seen to follow the style of Mr Crabb as a deal maker.

He is yet to give very much away on how he would tackle the Wales Bill, although he has been intimately involved with it right from the start as Mr Crabb's number two.

The question will be whether the new Welsh secretary will be able to achieve the consensus on the Wales Bill that evaded the MP for Preseli Pembrokeshire.