Finally got the prescription for it. Saw the pediatrician and got her note to say prescribe Movicol. Dropped the note into GP and got to chemist and was given docusate. So returned to GP and made appt and this time was prescribed movicol - for adults though. Finally have what I asked for though.
She actually drank the whole lot down in one go. Can't beleive it was that easy! After years of struggling with lactulose, docusate, laxitives, suppositories, and so on.
If this works I'm going to be the happiest mum, with the happiest DD. Finger crossed.