The Scottish and Welsh First Ministers have called for more time to scrutinise the new Brexit deal and potentially hold a second referendum in letters sent to Boris Johnson and Donald Tusk.
The joint correspondence, signed by Nicola Sturgeon and Mark Drakeford, described the Bill as among the most important pieces of legislation ever considered by the UK Parliament, the Scottish Parliament and National Assembly for Wales.
The legislation is due to be published on Monday, with the Prime Minister hoping a “meaningful vote” will be tabled on the Bill at Westminster on Tuesday.
Due to the Bill legislating on matters devolved to the Scottish and Welsh administrations, approval is needed from Holyrood and Cardiff before it can be passed.
The First Ministers letters have called for an extension to the Brexit process to be approved to allow time for the devolved administrations to scrutinise the Bill in detail.
In their letter to European Council president Donald Tusk, the politicians also pledged their support for a second referendum on EU membership, calling for an extension long enough to allow for a second poll which would have the option to remain on the ballot paper.
The letter addressed to the Prime Minister said: “We therefore wish to state in the clearest possible terms that we and our legislatures need time to analyse and consider the draft Bill.
“We share the view which lay behind the amendment passed by a clear majority of the House of Commons that the time between now and October 31 provides insufficient opportunity to undertake this essential scrutiny.”
The letter also called on the Prime Minister to “comply fully and in good faith” with the Benn Act – which legislated a request for an extension if a deal hadn’t been reached with the EU by October 19.
In their letter to Mr Tusk, Ms Sturgeon and Mr Drakeford said it would would be “simply impossible for us to fulfil our constitutional responsibilities in this timescale”.
The letter added: “An extension would allow us to adequately scrutinise the agreement and the draft legislation in accordance with our constitutional responsibilities.
“While clearly it is a matter for the council to consider how long such an extension should be, we would favour one which is long enough to enable a referendum with remain on the ballot paper to be held in the UK.
“Both of our Governments and legislatures are in favour of such a referendum and of the UK remaining in the EU.”