Question:
"Im replacing my front wheel bearings on my 78 leyland. (drum brakes) I fitted the new bearings and seals and went to fit in the drive flange and i noticed the seal is too big to seal on the flange. Is there a sleeve or spacer that the seal seals on?"

Answer:
"Yes there is a tapered collar that sits between the flange and the bearing.  You must have set them aside when cleaning things up!"  See Photos Below

Seal for front wheel bearings on Mini

Drum brake seal Mini Cooper