Sorry I realise its hard to see which branch Im talking about. Its the thick one at the front.

Don't cut it right down, but take it down just above one of those ridges you can see in the picture spaced periodically down the stem. Those are where new growth may come from, so angle your cut downwards to allow rain to run off and away. Where you cut it depends on where you need laxer growth to appear from, so if you want to train it on a trellis which is, say, 1 foot from the ground, cut it around that height. This should encourage at least one new branch to form, and that should be tied onto your support before it hardens off, like this one has done.

Many thanks Bamboo. Job done!