This evening, I took the honey/grape juice/raspberry juice mix and made it up to a gallon (well 5 litres really) and then took a reading to see what needed doing to it.
I was surprised that it was "only" about 1090, so because I don't want it too acidic and that raspberry can often be quite overpowering on it's own, I've just pitched Lalvin's 71B yeast.
71B only has a 14% tolerance but I'm hoping that it should ferment dry, I'll have to check the numbers to see what I need in total gravity drop to attain 14%. If I have to feed it a little more honey, then that's not an issue. The 71B was used dry as I don't want it to kick in too quickly, but also 71B can metabolise some of the malic acid from the raspberries.
So I'm hoping that when I get home on tuesday, it should be showing some signs of fermentation........