Subject Access Requests must be complied with in a timely manner and the ICO website contains all the information on that. To manage expectations, it's not uncommon for acknowledgements of receipt to take a few days to arrive. When it does arrive the acknowledgment should also contain the target date for supplying the information requested. I generally query if similar Requests have been received if I don't receive acknowledgment within, say, ten days. On a general note, requests to large organisations are often handled more efficiently than those directed at smaller ones which are unfamiliar with procedure. My correspondence with organisations is always polite and understanding (even if I'm seething) because ultimately people are involved in sifting, collating and responding and a little courtesy often goes a long way.