I have recently fitted a Torbeck valve to a toilet cistern, but
am suffering problems with a loud 'bang' from the pipework when
it shuts off.

Fit a water hammer arrestor, such as BES #11355 (www.bes.ltd.uk). You
install it next to any problematic suddenly closing valve (i.e. Torbeck,
ceramic disc tap, washing machine). It is basically a tiny pressure
expansion vessel that is capable of absorbing the flow of water that is
moving fast, but has nowhere to go when the valve closes.

Christian.