Brian Taylor
BBC Scotland Political Editor

Image source, Getty Images

This is a calamity, without caveat, for Derek Mackay, for the SNP, for the first minister and for the collective Scottish government.

One must also express sympathy for the youth who apparently received unwarranted and unwanted attention, together with his family.

To recap,the Sun newspaper has reported, external that Mr Mackay allegedly sent some 270 messages to a 16-year-old boy. Among those contacts, he is said to have called him "cute".

Mr Mackay has now quit as finance secretary - on the very day he was due to deliver his Scottish budget. Rival parties say he should also be removed from membership of the SNP.

• Scots finance secretary quits over messages to boy
• Who is Derek Mackay?
• Read more here

Efforts to tackle climate change and funding for health and education are to be key themes of the Scottish budget.

Minister Kate Forbes will set out tax and spending plans for the coming year after the resignation of Finance Secretary Derek Mackay.

The budget process has been pushed back by December's snap election and a delay to the UK government's own plans.

Mr Mackay stepped down after a newspaper allegation about social media contact with a 16-year-old boy.

• Scottish budget: what do you need to know?
• Watch Ms Forbes's speech on Holyrood Live from 14:40

Image source, Getty Images

Kate Forbes has been the MSP for Skye, Lochaber and Badenoch since 2016.

The 29-year-old is from Dingwall in the Highlands, but spent time in Glasgow and India as a child and teenager.

The fluent Gaelic speaker studied history at Cambridge University, going on to Edinburgh University. She then worked as an accountant in the banking industry before being elected as an MSP.

She was appointed as a minister for public finance and digital economy in June 2018.

Glenn Campbell
BBC Scotland's Chief Political Correspondent

Derek Mackay's political star was rising. And now it has come crashing down.

He's quit the Scottish cabinet on the day he was due to deliver the budget, presumably taking any prospect of becoming first minister with him.

It is a major setback for the actual first minister, Nicola Sturgeon, to lose such a key minister at such an important moment.

Her party will also need to consider whether or not Mr MacKay can continue to represent the SNP.

Image source, Andrew Cowan

After thirteen years in office, the SNP does not have its troubles to seek.

There's the CalMac ferry order scandal, a public inquiry into hospital failures and a full review of the school curriculum amid concerns about under-performance in education.

And the party's former leader, Alex Salmond, is due to stand trial next month on allegations that he sexually assaulted ten women, which he denies.

Yet the SNP continues to dominate its rivals in opinion polls, which also suggest support for independence has risen since the 2014 referendum to around 50%.

In Scottish politics post-Brexit the SNP have, so far, been incredibly resistant to the effects of political gravity.

Image source, bbc

Scotland's finance secretary has quit hours before delivering his budget amid reports that he messaged a 16-year-old boy on social media.

The Scottish Sun said that Derek Mackay contacted the boy, external over a six-month period, and told him that he was "cute".

Mr Mackay said he had "behaved foolishly" and took full responsibility for his actions.

And he apologised "unreservedly" to the boy and his family.

First Minister Nicola Sturgeon is due to give a brief statement in the chamber before FMQs and Public Finance Minister Kate Forbes will deliver the budget from 2.50pm.

Read more here.

Scottish Conservative interim leader Jackson Carlaw has just called on Derek Mackay to resign, saying what he did was “grooming.”

Former SNP minister Alex Neil has spoken of his shock and described it as a “tragedy.”

Philip Sim
BBC Scotland political reporter

Derek Mackay's resignation cuts short what was a meteoric rise through Scottish politics.

He was elected a councillor in Renfrewshire in 1999 at the age of 21, and went on to lead the council for four years.

He became MSP for Renfrewshire North and West in 2011 and was made local government minister by Alex Salmond later that year.

When Nicola Sturgeon took office in 2015, he became transport minister, before being promoted to finance secretary following the 2016 Holyrood election. Many bookmakers had him down as the favourite to succeed Ms Sturgeon as first minister.

The 42-year-old was also a major figure in the SNP, serving as business convener for seven years, a role which saw him overseeing management of the party and chairing conferences and election campaigns.

Derek Mackay said: “I take full responsibility for my actions. I have behaved foolishly and I am truly sorry.

“I apologise unreservedly to the individual involved and his family.

“I spoke last night with the First Minister and tendered my resignation with immediate effect.

"Serving in government has been a huge privilege and I am sorry to have let colleagues and supporters down."

Image source, bbc

Accepting Mr Mackay’s resignation, First Minister Nicola Sturgeon said:

"Derek has taken full responsibility for his actions and apologises unreservedly for them to the individual involved and to those he has let down. He has submitted his resignation as a government minister which I have accepted.

“Derek has made a significant contribution to government, however he recognises that his behaviour has failed to meet the standards required.

“The Minister for Public Finance, Kate Forbes, will present today’s Scottish Government budget setting out our actions to support the economy, back our people and public services and tackle the climate crisis, and that remains my government's focus.”

Douglas Fraser
Scotland business & economy editor

It's a budget, but not as we know it. Kate Forbes, a late replacement for Derek Mackay, will get to her feet on Thursday afternoon, with a lot of pencilling, and the hope of ink next month.

The finance minister doesn't know what size the Holyrood block grant will be for the start of April. And while forecasting income tax always requires a bit of guesswork, this time will involve more peering into the cloudy crystal ball than usual.

Why? Brexit, of course. And the change of leadership in Downing Street.

Read Douglas Fraser's blog on the Scottish budget

Image source, Getty Images

Kate Forbes has been the MSP for Skye, Lochaber and Badenoch since 2016.

The 29-year-old is from Dingwall in the Highlands, but spent time in Glasgow and India as a child and teenager.

The fluent Gaelic speaker studied history at Cambridge University, going on to Edinburgh University. She then worked as an accountant in the banking industry before being elected as an MSP.

She was appointed as a minister for public finance and digital economy in June 2018.

Image source, bbc

Efforts to tackle climate change and funding for health and education are to be key themes of the Scottish budget.

Public Finance Minister Kate Forbes will set out tax and spending plans for the coming year after the resignation of Finance Secretary Derek Mackay

The budget process has been pushed back by December's snap election and a delay to the UK government's own plans.

Mr Mackay stepped down after a newspaper allegation about social media contact with a 16-year-old boy.

Read more here.