Hi Roy, this is the P3 cut or Diamond cut which first appeared (together with the revised P1 and P2, with a higher dome) as part of the new era of Whitefriars paperweights in late 1969. This happened just before Whitefriars developed the Whitefriar symbol, cane and date cane. This ties it down to mid / late 1969 as towards the end of 1969 Whitefriars first engraved "Whitefriars 1969" on the base and then added a "lone Whitefriar" cane i.e. No date. Eventually in early 1970 the full Whitefriar with date cane appears.
The P3 first appears in a 1970 catalogue although they were being made in 1969. Your example is A VERY EARLY example of this cut and could be thought of as experimental, although I would suggest it is more accurate to regard these as early prototype / production examples.
I have added a photo of a similar item with a lone Whitefriar.
Cheers,