I have the opportunity to apply for a small grant (probably under £300) to spend on any costs associated with my PhD. I am otherwise self-funded - I receive no research council or university funding. One of the conditions of applying for the grant is that, if I am awarded it, I must acknowledge the awarding body in all papers I write during my PhD, and in my thesis. I was wondering if this is a typical request?

Yes, it's normal for some types of funding for sure. You have to state your funding if its from one of the research councils, for example. It just needs to be a brief line, saying something like "this research (or Joe Bloggs) was supported by a small grant from Name of Organisation (reference no. of grant if there is one)."

The only scenario where I can see this being an issue would be if you had received lots of small pieces of funding from various places, as it might seem a bit bitty listing them all. I've seen two or three listed before but not dozens.

Hope this helps.