Nicola Sturgeon demands summit with David Cameron over Scotland Bill

Ms Sturgeon states that the “conduct of this negotiation is a matter of increasing public concern in Scotland” as she suggested that Chief Treasury Minister Greg Hands, the UK government’s lead in the talks, is not serious about reaching a deal with Scottish ministers.

In an upping of the stakes by the Scottish Government, Ms Sturgeon offers to meet Mr Cameron in London on his return from talks in Brussels over the UK’s terms of membership of the EU.

The Scottish and UK governments are in dispute over the adjusted formula for Scotland’s block grant, with each side insisting their preferred formulas would be to the detriment of Scotland or the rest of the UK respectively.

However, Ms Sturgeon, in a hardening of the Scottish Government’s language, suggested that the Prime Minister will have “failed to honour both your pre-referendum Vow and your commitment to implement in full the recommendations of the Smith Commission” on delivering new powers for Holyrood if it continues with the same approach.

In her letter to the Prime Minister she states: “I appreciate that you are heavily engaged this week with EU negotiations - and understandably so - but I feel I have no option but to seek your attention on this matter.

“Since the conduct of this negotiation is a matter of increasing public concern in Scotland, I have again concluded that I should make this letter available publicly.

“Though time is running out, I remain committed to reaching an agreement. However, if we are to do so we must make substantial progress - and see significant movement from the Treasury - in a short space of time. I hope you will be prepared to intervene to make sure that this happens.

“The Deputy First Minister remains available to travel to London at any time this week. If it will help to bring matters to a conclusion, I would also be willing to meet with you in London on your return from the European Council.”