Am about to change the chain on my Orange P7 single speed. The chain on it is a SRAM, with 'PC30' marked on the links.

Without having the details with me, I bought a SRAM chain marked 'PC1' last year. Can I use this as a replacement ?. It's properly stickered by SRAM as being single speed compatible, but is a little wider than the original chain. Will it still be okay to use, or is this a mistake that cost me a few quid and I need to stick with a PC30 chain.

You can use the PC-1 but in my experience they're a crap chain and seem to break far too easily.
KMC 610-HX is far superior in my opinion.