I bought a property in december last year for buy2let purposes and my sister needed to move in and has been there ever since and is paying the mortgage on it, i have to put a fiver each month to make up the shortfall due to mortgage increases lately,do i need to inform the inland revenue or somewhere?
I suppose so, yes. Her paying the mortgage is really her paying you rent. You are gaining income from having here there, so IR should be informed. Get a decent accountant and you'd be suprised how little tax you'll have to pay!