So lets work with what we have.
Nervex lugs, but only on headtube and seat tube.
5 digit serial number.
Pointing to one of two possibilities so far, both mass market.
One is 1960-63 Raleigh, the other is similar age Peugeot.
I think what would seal it is what the BB thread is, if French then Peugeot, if Raleigh or British, then Raleigh...