What they appear to be talking about is a restriction on the Scottish Ministers making regulations concerning devolved aspects of Universal Credit. Here is what the Smith Commission said about it:
"43. Universal Credit (UC) will remain a reserved benefit administered and delivered by the Department for Work and Pensions (DWP). Within this framework, the Scottish Parliament will have the powers outlined in paragraphs 44 to 45 in relation to UC.
44. The Scottish Government will be given the administrative power to change the frequency of UC payments, vary the existing plans for single household payments, and pay landlords direct for housing costs in Scotland.
45. The Scottish Parliament will have the power to vary the housing cost elements of UC, including varying the under-occupancy charge and local housing allowance rates, eligible rent, and deductions for non-dependents
46. The power to vary the remaining elements of UC and the earnings taper will remain reserved. Conditionality and sanctions within UC will remain reserved."
The key points are therefore as follows:
1. Universal Credit is to remain, generally, a reserved matter, administered mostly by the UK Government's DWP.
2. The Scottish Government is to be given some flexibility in certain administrative and minor policy provisions in relation to it.
Now let's look at the provision in the Scotland Bill to which this "veto" relates. It appears to relate to the power to make regulations in respect of how much housing benefit someone is entitled to, who it's to be paid to, and how frequently. Pretty dry stuff. Sections s24(4) and 25(3) are the ones that contain this so-called "veto" power. Their wording is identical. It is as follows:
"The Scottish Ministers may not exercise the function of making regulations to which this section applies unless—
(a) they have consulted the Secretary of State about the practicability of implementing the regulations, and
(b) the Secretary of State has given his or her agreement as to when any change made by the regulations is to start to have effect, such agreement not to be unreasonably withheld."
The wording of this, to me, seems pretty clear. The nature of the duties and rights here do not relate to whether or not a set of regulations may be made, but when their implementation should take place. It is an administrative function to ensure DWP is ready to alter Universal Credit payments in line with whatever regulations the Scottish Government decides to make. This explains the consultation on the "practicability" of the "implementation" of the regulations in sub-clause (a), and suggests that the requirement to consult does not relate to whether or not any change should happen. This is re-enforced by sub-clause (b) which restricts the Secretary of State's ability to withhold agreement "as to when any change made... is to start to have effect".
This is important, because it means when Stewart Hosie said, on the Daily Politics earlier today:
"If the Secretary of State, the sole Tory left in Scotland, decided not to give his agreement, for whatever reason, he or she has a de facto veto and therefore the spirit of the Smith Commission is breached before we even get going."
He was wrong. Firstly, because refusal cannot be "for whatever reason". It must relate to the practicalities associated with the timing of the implementation of the regulations. This is not a veto. If the Secretary of State refused to give his consent because he or she disagreed with the principle of housing benefit payments being increased, or made more frequently, his or her decision could be subjected to legal challenge as using a power for an improper purpose, or for taking into account irrelevant considerations, two well-established common-law grounds for judicial review, and ordered to be retaken.
This is re-enforced further by the second part of the sub-clause, which provides that "such agreement [is] not to be unreasonably withheld". This, in effect, means that if the Secretary of State is to withhold consent, he or she must be able to show that it was reasonable to withhold consent with respect to the timing of the implementation of the regulations. He or she would likely need to show evidence of administrative difficulties meeting the demands of the Scottish Ministers' regulations from the DWP, and failure to do so might additionally have the decision struck down by the courts for irrationality if no such obstacles can be identified.
If the Scottish Government's powers with respect to Universal Credit were to be administered by a Scottish Government Department, it might be reasonable to say that consent in some form of the UK Government was unnecessary and unreasonable. This is not, however, what the Smith Commission proposed. It proposed that Universal Credit be a matter for the Department for Work and Pensions. This provision is one intended to facilitate logistical integration between Holyrood regulations and Westminster departments. It's not a political ploy to stop Scottish politicians implementing different welfare policies from the rest of the UK.
Put at its simplest: this is not a veto. This is what Smith promised.