Anglophile, I've had a look at what the Stanley Gibbons catalogue says on the varieties of this 6c orange:
Perf 10:
Sg 601 (Oct 1968) - no phosphor or fluorescent paper - catalogue value of 10p used.
Sg 601p (Nov 1968) - two phosphor bands - catalogue value of 85p used.
Perf 12.5x12
Sg 606 (Mar 1969) - no phosphor or fluorescent paper - catalogue value of 10p used.
Sg 606p (Mar 1969) - two phosphor bands - catalogue value of £1.25 used.
The 6c orange doesn't actually exist in perf 12 according to Gibbons, only P10 or P12.5x12
So all in all not very valuable but hey stamp collecting is all about the interest in these subtle varieties!
