I live in Brighton and the vast majority of people I know use http://www.just-eat.co.uk/ which is basically an online wrapper for ordering takeaways. It covers loads of the local places and you usually get free delivery within a ~2 mile radius for orders over £8 or a ~£3 surcharge for delivery. You can order pretty much any kind of fast food from there, although the big companies (McDonalds, etc) don't deliver.