The maximum surgeons can offer is 800cc but I think this may be at one time, so if you wanted larger it has to be done through 2 or more separate operations. From what I’ve read the biggest overall size you can get with silicone implants is 1500cc, after that you would need saline implants doing instead.
This is only from what I’ve read here on the forums though so book a consultation or ring them and ask! x