California X New Zealand rabbit is often quoted as the best cross breed for meat. It's almost like a magical combination in the minds of some people.
There is a catch. You must have a good Calif and a good NZ to breed together to get the best effect of the cross breed vigor.
You also have to maintain separate lines of Cals and NZ to cross for meat. So you have to select breeders from two different breeds to maintain separately for your meat crosses.
Instead, I suggest using a single meat breed of rabbit and using selective breeding to develop your own bloodline of highly productive meat rabbits.
In UK, I would look at a meat breed like the Beveren. Raise them for production standards with linebreeding and eat or sell the culls.
When you develop a line of rabbits that reliably produce large, healthy litters you will find people searching you out to buy rabbits from you for breeding.
Have a good day!