Retention Swing vs Universal Swing (Lib Dem Surge)
It does appear that the traditional UNS methodology for seat projections cannot cope with a Lib Dem surge.
I have done some calculations on a retention swing. That is a calcalation on the basis that in each seat the national transfer of votes is replicated. However, if Labour have lost a third of their votes nationally they lose a third of their votes that were cast previously in each seat rather than the same percentage of the total vote in each seat.
This is a more complex calculation, but it produces more reliable results.
It needs more work, but a first cut of the data is available here