On a Renault Clio 1.2 16V 2002, what is the lump immediately between the engine cover and the firewall?

On the Renault Clio 1.2 16V, 2002 model, there is a silver top to the engine (which the oil filler is recessed in to). At the back of this there is a block about 10cm across and 7cm wide, which appears to be loose. There is an electrical connector to it, on the right hand side (looking in to the engine bay from the front of the car). Any idea what this block is, and how concerned I should be that it's loose?