Single day bike insurance.

[Dave48]

If you cant/wont take out (comprehensive?) insurance for the new bike, its simpler and better all round to hire a van specifying tie down loops fitted. One days hire and you can then take out "laid up" ins cover until you decide to start using on the road. The problem with riding other bikes (NOT OWNED BY YOU) is the level of cover provided-resd the small print!-usually just 3rd party risks. Presumably with a bike worth £3-£4 thou you don't want to be cutting corners(excuse pun!) with level of cover.
Good luck & let us know what you decide.