Favour seems to fall on proper keys now rather than the round key type - something "Sold Secure" should be good - quick scan of the Hein Gericke catalogue threw these up -
Oxford Enigma - this is a big disc lock that can be used as a padlock - sold secure Gold and thatcham approved - £49.99
they also have a Boss disc lock ("U" type ) again Sold secure
£34.99
They do a device called Defiance - Fcuk off big ground anchor with crossbar and Enigma lock for £149.99
ABUS Granit disclock / padlock ( 11mm steel shackle which could not be broken open in tests ) £52.95
Maximum security ABUS Granit 12mm 1.1M hex chain and Granit plus padlock - £103.95
WWW.hein-gericke.com 0800 165 165 for a catalogue
Search for Zanx thread on making a ground anchor out of a concrete block as well.
Owner of the most immaculate motorcycles since 1979 .... 