The first opinion poll in the aftermath of Boris Johnson becoming Tory leader and Jo Swinson becoming Lib Dem leader was always going to be a moment of truth, because there was a reasonable expectation that there would be a honeymoon effect for Johnson, as has been the case for previous new Prime Ministers. The fact that doesn't seem to be happening may effectively seal the Tories' fate in the Brecon and Radnorshire by-election next week.
Britain-wide voting intentions (YouGov):
Conservatives 25% (n/c)
Liberal Democrats 23% (+3)
Labour 19% (-2)
Brexit Party 17% (-2)
Greens 9% (+1)
SNP 4% (n/c)
Plaid Cymru 1% (n/c)
UKIP 1% (+1)
Scottish subsample: SNP 42%, Liberal Democrats 18%, Brexit Party 13%, Labour 11%, Conservatives 10%, Greens 5%
It's odd that Jo Swinson does appear to have boosted the Lib Dem vote given that she had far less airtime on Monday than Johnson had yesterday, but probably what's happened is that a small Boris Bounce has been factored in for a few weeks, because everyone was aware that he was going to become leader. If that's right, the boost has been extremely modest - only a few percentage points. Swinson is more of a novelty for people, which would explain why the Lib Dem bounce has happened at the actual moment of the leadership announcement.
Although YouGov's Scottish subsamples can be regarded as more meaningful than those of other firms (because they're properly structured and weighted), it would still be a mistake to take changes from one subsample to the next too seriously, because the small sample size means that any increase or drop in support for a party is more likely to be an illusion caused by normal sampling variation. However, on the face of it, the Lib Dem vote has increased in Scotland at the expense of unionist parties and not the SNP - which would be the dream scenario. If that pattern holds, we could see the Lib Dems splitting the unionist vote in a way that actually helps the SNP gain seats from the Tories.