Its hard to explain but basically... a girl is in uni and dies and her friend takes her place and returns home in a wheelchair as the dead girl reckons there's dodgy goings on at her fathers house... anyway.. they father , grandfather has been killed and is in the bottom on the pond tied to a chair or swimming pool... it's a real scary sight as his long white hair is flowing in the water and he is very very old.. the couple who have killed him live at the house and have never met the granddaughter which is why the imposter can be an imposter.. anyway.. the end scene is where the wheelchair is perched on the end of a cliff and so the bloke of the couple who murdered the grandfather pushes it over.. but as it goes over the occupant turns and its his wife who was sat in it not the imposter granddaughter... great ending.. anyone know..

Scream of Fear (or Taste of Fear). Go to the "how does the movie end' link on this page - it pretty much repeats exactly what you described...
Scream of Fear (1961) - FAQ (http://www.imdb.com/title/tt0055505/faq?ref_=tt_faq_sm)

Oh thanks.. I thought itbhad the wprd fear in it... However, I presumed tjat I was mistaken and that it must have been shown as part of the appointment with fear season they ised to show... Great anyway.. Many thanks

Sure :)