Unfortunately the hose wasn't screwed in, it was a solid compression fitting. My partner solved the problem by fabricating a single piece of brake pipe (left over from building his trike). He has a flaring kit, so cut off the fittings on the old pipe and put them on the new one. After much cursing and swearing, taking out the driver's seat, all the foot pedals falling apart, he eventually got it all fitted back together, and it works brilliantly. He says he needs to bleed the system again to make sure there's no air left, but we've been using it since July 29th.
Thanks for all your suggestions.
Jacqui