Thanks for the post, however.
I think I said that the vice that broke was my Dads old one so had a lot of sentimental value, as I was taking a day off work today I spent some time looking at the possibility of repairing it.
After about 5 hours of labour, some 6mm steel plate and 8 M8 Bolts & Loctite it is now fixed.
The casting had only cracked and had not broken in two so I simply put a 2 6mm thick plates held in place with M8 bolts accross the cracks.
Did it up murder tight and seems to hold OK - reckon it might see me out now.