As I posted (and Kezo mentioned) on your other postings, the IHD will be reading at peak rate, so say 60p standing charge plus usage,
60p standing charge plus 13kWh at about 28p would equal around £4.48 or thereabouts depending on your other usage during that time.
Please excuse spelling/typos. Apart from being a clot it turns out I had one on my cerebellum that's now causing various problems!