I'll admit, it is an odd shape, but Voltan may be correct in calling it a tow bar - many British vehicles had one constructed from leaf springs & put between the hard towing points, used for pulling trailers (& in the Centurions case, a fuel bowser, given that they were quite thirsty.
Here's a pick of the Duxford one, it's not exactly the same, but I can't think what else it could be (are there any attachment points on the rear of the model?).