In the post Eastleigh celebratory glow, Shetland MSP used his Scotsman column to issue a sharp challenge on the economy and welfare reform to Liberal Democrat MPs.

First, he praised the party for the way we had come together to win against the odds.

 A personal party scandal was badly handled from beginning to end. The Tory press scented blood and threw themselves at the Lib Dems.

But the Lib Dem by-election machine still has a kick. A win was needed and secured. Morale is on the up and belief returns. This will grow if Lib Dem Westminster MPs now get really stuck into delivering the changes to coalition policy the country needs and wants.

So, what are these changes, then? First, on the economy:

Chancellor George Osborne will have to explain why, when he said the triple-A rating for the UK economy was the most important test of his economic policies, he did not mean it. The credit ratings agencies were the very people saying all our banks were in perfect health before the 2007 crash. Why Osborne put so much store in their opinion is unfathomable. His credibility is holed.

This is an opportunity for Lib Dem Business Secretary Vince Cable. He has been pushing for a massive jump in capital investment to boost the economy: spending on roads, railways, hospitals and a whole lot more.

Investment in the UK economy to create jobs is badly needed and long overdue. Sensible economists and leaders of industry are delivering a pro-growth message to the Treasury. Surely the coalition will accept that the current strategy needs revision in the face of overwhelming evidence. Lib Dem MPs should push the growth door open.

And then welfare reform:

Few dispute the need for reform of welfare. But some elements of this, notably the “bedroom tax”, appear callous and aimed at the very people who should have some modicum of state support.

So, emboldened Lib Dem MPs whose mailbags reflect growing unease about welfare reform should make a progressive case. They are helped by the Tories appearing to be split. They all want cuts to public spending, but many Tory ministers are defending their areas.

Those two things, says Tavish, should be the legacy of Eastleigh. You can read the full article here.

* Caron Lindsay is Editor of Liberal Democrat Voice and blogs at Caron's Musings