Thanks for the replies.
Sorry, I should have said in my first post that the aircraft will be flying trans-Pacific as well as trans-Atlantic. Even with locker tanks it will still need ferry tanks. Longest over water leg is in excess of 10 hours.
HS125... thanks for the tip, I will contact them to see if they can help. I am also in contact with Far North Aviation in Wick, who appear to know a lot about ferrying. It might be logistically easier to use Biggin, but will keep our optiosn open.
Many thanks
Jim