Victoria
I'm afraid this is not an area that we advise on so your really need to get face to face advice from a trained advisor. Do an internet search for "welfare advice" with your postcode, town or county.
I do not think it should be a problem as you appear to be reducing your mortgage, I suspect that you cannot really tell them until you exchange contracts.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems