I enquired about going larger than 100A on our (still pending) fuse upgrade and they said they'd be happy to install 3-phase but the cost starts at £8k if everything is already in order and can go up from there if they need to do anything non-standard.
I thought it would be pricey. Good to know though. I've only worked in one domestic place that had it and they kept blowing a fuse in the street. It was a 7 storey place in Mayfair.
You have 3 phase in your house? Most UK installations are single phase.