Shipping to UK
I sent mine back from Joburg to UK (Manchester) by air freight.
Cost-wise there's not a huge difference between air and sea if you take everything into account.
Sea freight arrives in the South and you need to get there, then unpack and get back: that all costs.
Plus takes time.
One hassle with air freight is you now need to drain and flush the fuel tank. I did that myself (just used water). Then wrote a letter on a nice looking letterhead and signed it saying it had been done (BMW Tank Flushing Services seems a nice name...). But perhaps your agent can do this paper-work part for you. But flushing with water is no problem: doesn't hurt anything. Need to take the tank off the bike though to do it.
And they do not let you send the battery with the bike, even disconnected. Or else it's classed as a higher hazard and costs a bit more to ship.
Another issue is your crate. In order to reduce size for the air freight, I made my own crate, and reduced the size of my bike by taking off front-wheel, handle-bars etc. But is a hassle, as well as harder to hold upright securely. And costs money to make a strong crate. Better option is go to BMW and get (even buy if they ask) a used crate that a new bike has arrived in.
Is a bit bigger, and thus costs a bit more, but if you have extra stuff you can pack that in.
You have to pay to get your crate fumigated.
To do all this you need a shipping agent: but as you can see there are lots.
Clearing in UK needs an agent, but you can pick that up the day you go to get the bike. Just visit the freight depot, find an agent (there are LOTS of companies), give them the paperwork and they clear it right away. You then take your crate to the Customs guys with your Carnet and with me they just stamped it in. Didn't bother to inspect it.
I found it easier to rent a small van to load the bike crate in and then drive away with it. The freight forwarder has a forklift and can load it in: make sure you get a big enough van heightwise to allow that.
The other end you can stop off at a place with a forklift to repeat the process of removing the crate from the van. Then unpack everything, rinse petrol tank with petrol to get rid of water traces, install new battery and is good to go. With a bit of help you can put the bike back into the van and drive all of it to wherever the van needs to go. Or else need a 2nd driver.