Muntons, along with other brands, sell Beer Enhancer, which if I remember correctly is 50-50 DME and maltodextrin. The DME will act the same way as sugar, but unlike sugar will contribute to taste, and the maltodextrin will add body and mouthfeel to your beer.
its worth bearing in mind that the maltodextrin, as far as I'm aware, is not really fermentable (which increases the FG, which is what increases the body), so you need to work this into your recipe. for example, if it calls for 1KG of sugar, I would consider using 1KG of the beer enhancer plus 500g sugar.