Why is Nicola Sturgeon resigning and what happens next?

After more than eight years in the role, there had been growing speculation that Nicola Sturgeon may step down as First Minister after the next Scottish Parliament elections, but such an abrupt resignation has come as a shock.

Widely regarded as one of the savviest and best political communicators in British politics, she ensured a smooth transition of the SNP leadership in 2014 when she took over from Alex Salmond, and has gone on to achieve success at every election since.

Nicola Sturgeon has continually pushed for Scottish independence, and her departure is undoubtedly a blow to the campaign for a second referendum.

Reasons for her departure will soon become clear but the First Minister has suffered a series of recent setbacks including a row over trans-rights and defeat in the UK Supreme Court over her plans to hold that second poll on independence. Recent opinion polls have shown a drop in support for Scotland going it alone.

She may simply though have had enough. Attention will quickly turn to her successor, with no obvious candidate waiting in the wings.

It was one of the biggest news stories of our time - and it's still not over. So what did Boris Johnson know about Downing Street’s notorious parties? With fresh revelations from our Number 10 sources, in their own words, listen to the inside story...