Warning draft Wales devolution bill 'problematic'
Plans to give the Welsh government extra powers are "problematic", open to legal challenge, and will cause even greater uncertainty in Cardiff Bay, a constitutional expert has warned.
The draft Wales Bill offers more say over energy, transport and elections.
But Prof Richard Wyn Jones of Cardiff University said there were still uncertainties which could lead to court battles between Wales and Westminster.
He warned against "legislating in haste" for another failed settlement.
Prof Jones is one of the authors of a report assessing the UK government's devolution plans, to be published by Cardiff University and University College London on Monday.
In 2015, the same team warned proposals for a so-called "reserved powers" model of devolution for Wales were unlikely to be workable.
Reserved powers is a change in approach to devolution, by which responsibility is assumed to be devolved in all matters except those specified as staying at Westminster.
There have been complaints the list of powers kept back by the UK government is too long, but Welsh Secretary Stephen Crabb has already said he is open to changes.
Speaking to BBC Radio Wales' Sunday Supplement programme, Prof Jones said there were "some really big changes from the White Paper to the draft legislation".
"We think that these add to the problems and further undermine the aims associated with the reserved powers model which is to make things clearer, more robust and more stable.
"It creates lots of uncertainty and arguably lots of scope for Supreme Court challenges - we've had three of those of course since 2011.
Prof Jones said Wales "craved stability" but claimed the draft bill failed to deliver it.
"It would actually be good not to talk about the constitution for a few years but that's not going to happen if there's real uncertainty about the powers of the assembly.
"The idea of legislating in haste to establish another dispensation which we know will also fail seems like a waste of everybody's time."
Welsh Conservatives leader Andrew RT Davies said: "This is our opportunity to get devolution right and takes us towards a lasting settlement."