Urgently Need A Part Name

TD5 Defender 110.

I need to get this fixed before tommorrow midday so I can get it down to the garage for my body panels to get fixed following the vandelism that occured last weekend. If anyone can help me out I'd be eternally grateful.

Its the pulley furthest right (looking from the front) on the auxiliary drive belt of the TD5 engine. It looks like its just a tensioner pully. I can replace it easily as its just a bolt. But I don't know what the part name is? Can anyone help?

Thanks