The polling does seem to show some tightening, but where is this happening? I highly doubt it's even across the country. If Labour is gaining in Scotland at the expense of the Tories, any seat gains there will just end up being at the expense of the SNP. I don't think the possibility of a hung Parliament happens unless the Conservatives fall below 40%.
Subsamples are always dodgy, but recent polls have shown that Labour is not significantly gaining in Scotland (every recent poll I've seen still has Labour 3rd there). Labour is mainly gaining in the North (Lab +14 in YouGov, +8.5 in Survation), Wales (Lab +19.3 in Survation, no sample from YouGov), and London (Lab +10 in YouGov, +7.3 in Survation).
As for which parties Labour is taking from, they could be taking from any mix of Lib Dems, Tories, UKIP, or Greens, depending on the pollster.
Links:
https://d25d2506sfb94s.cloudfront.net/cumulus_uploads/document/wvyc3lofp5/SundayTimesResults_170519_VI_W.pdfhttp://survation.com/wp-content/uploads/2017/05/Final-GMB-GE2017-III-Tables-190517TOCH-1c0d3h4.pdf