Do you know of any cargo shipping companies sailing from the u.k that take passengers?

Yes, the RMS (Royal Mail Ship) St.Helena which supplies the tiny islands in the mid Atlantic which are crown dependancies also accepts passengers. It also stops off at familar holiday destinations like Tenerife along the way.

http://www.rms-st-helena.com/

I think most cargo ships have provisions for a handful of passengers, but don't expect any organized activities. On TV once, they profiled going on cargo ships and one lady brought along her sewing machine and plenty of fabric so she wouldn't get bored.

Yes, try Maris Freighter Cruise company they have many different cruises available on commercial freighters to all destinations and of different durations. Am going to Australia NZ next year which will take about three months departing and returning to Tilbury.

Contact Lloyds of London for an up to date list

you can get a lot of information here

http://www.cargolines.biz/FAQ.htm