12a Opening of public bar, distinguished scientists in jumpers (8)
_ RA _ CERS
It looks like PRANCERS but why?
27d Short poem? Sounds like a whopper (4)
_A _ A
The first letter is W if AJWAN is correct for 26a
26a Source of oil from Japan, sealed in a pasty (5)
Is this AJWAN ? = J(apan) "inside" a wan (pasty)
AJWAIN is a source of oil, but is AJWAN an alternative spelling?