When I was applying (would have been five years ago now), the GEM courses at King's and Newcastle both accepted arts graduates and didn't require Chemistry A-level; nor did they grill you on A-level Chemistry at interview. There may have been other GEM courses that accepted arts graduates, but those two definitely did because I was offered interviews at both, and I was an English Literature graduate without the full Chemistry A-level. I did have a ****-ton of work experience though (as in, several years' worth) - be prepared for them to expect more from you on that front, since you'll have had more time to accrue experience than the average 17-year-old applicant. I have a feeling that King's may have changed their entry requirements since I applied, but you'll have to check on the individual universities' websites.
I went for a five-year course in the end, and I'm glad I did - though unfortunately the fee increases since then have made that an extremely difficult option unless you're made of money. It would broaden your options though, so it's something worth considering.