First, here's the average of the last poll before the second debate from 10 polling firms. Of these 10 firms, 7 have already conducted a poll after the second debate; the pre-debate average of these 7 firms is in parentheses.
CON - 31.9% (31.9%)
LD - 30.5% (30.3%)
LAB - 26.4% (26.7%)
Here's the post-debate average, with change from the pre-debate 7-firm average in parentheses:
CON - 34.3% (+2.4)
LD - 29% (-1.3)
LAB - 26.6% (-0.1)
These post-debate numbers give, according to UK Polling Report (change with respect to pre-debate 7-firm average in parentheses):
CON - 270 (+31)
LAB - 254 (-14)
LD - 95 (-17)
Other - 13 (0)
The Tories have taken the lead, but do not have a majority. The usual caveat still applies: Labour is likely to get fewer seats than predicted by a uniform national swing, while the Lib Dems and the Tories are likely to get more. It looks very likely that if an election were held now, the Conservatives would be the largest party, followed by Labour and the Lib Dems.
Could a Labour-Lib Dem coalition arise? The above prediction gives them 349 seats, against 270 for the Tories and 31 for others (13 from GB + 18 from Northern Ireland). But in reality, Labour-Lib Dem should get fewer than 349 seats. If they fall below the majority threshold (theoretically 326, but in practice around 323 due to Sinn Fein not taking its seats and the Speaker not voting) without the Tories rising above it, Labour and Lib Dems would need the support of small regional parties. Alternatively, the Tories could try to woo the Lib Dems or maybe the small parties into government.
The UK could also get a minority government like in Canada. I doubt Labour would try, or be able, to stay in power without a formal coalition if they finish third in popular vote. However, as the largest party, the Tories could try to do that.
This election will be fascinating to follow!