Ask HN: UK SIM card

I'm headed to the London in July for my honeymoon. My fiancé has a U.S. Verizon iPhone 6 and I have a Verizon iPhone 6 plus. We're looking at all the different plans to get a local SIM card for emergencies and if we get seperated. I'm hoping to get some expert advice on the plans/providers. And I've read both phones support the UK gsm network but I'm hoping that someone can confirm. Thanks!