It would be fascinating to sit in on the informal meeting now planned between the Scottish Parliament's Welfare Reform Committee and Westminster secretary of state for pensions Iain Duncan Smith, on March 27th.

Unfortunately the meeting will not take place in public, instead taking the same form as the similar meeting the committee held with the UK Government's Lord Freud in November.

Amid concerns about the far-reaching changes involved in the new Universal Credit benefit, anxiety over medical testing of claimants, the introduction of Personal Independence payments for disabled people and fears over the impact of the "bedroom tax", MSPs have repeatedly asked Iain Duncan Smith to show up and give evidence. In fact, an invitation has so far been issued four times.

The standard response from the Department for Work and Pensions is that Mr Duncan Smith is answerable to the Houses of Parliament, not Holyrood.

So the fact that he's now agreed to come and at least talk informally is something of a breakthrough, and with claims this week from Duncan Smith's Labour Shadow Liam Byrne that Universal Credit is in "meltdown", you could argue it comes just as things are really hotting up.

Universal Credit is due to be delivered at the end of April, with wider national roll-out beginning in October. But, according to Labour, some of the private firms contracted to help deliver the changes are muttering behind the scenes that it is in trouble.

Members of the Welfare Reform committee have already met to discuss their approach to questioning the secretary of state and are likely to use the time to try to pin him down on key questions of concern.

These include the reasons why the bedroom tax makes insufficient provision for people with disabilities who need an extra room for equipment or carers, and why it penalises foster carers who have a spare room vacant when they are not currently caring for a child.

They will almost certainly ask why Northern Ireland has been permitted some flexibility in the way Universal Credit is administered, while Scotland has not.

And they may try to introduce questions submitted by members of the public in the committee's own Your Say sessions, such as the questioner who asked whether it was right to withdraw benefits to force disabled people back to work, when there was little strategy or financial support to help them find jobs.

However Mr Duncan Smith is expected to keep the meeting short, and the Welfare Reform Committee is looking into seven aspects of benefit change, its clerk has warned members they may only have time to cover three or four areas in any detail.

The previous meeting with Lord Freud was not minuted, but follow-up questions were put to him by letter and responses to those made public. The same is likely to happen with any follow-up clarifications submitted to Iain Duncan Smith, so it will be worth looking out for those. Look out too for public statements from members of the committee, who are likely to make clear their thoughts as soon as the meeting ends.