Sharia accounts – in accordance with Islamic banking principles – prohibit interest. Instead, they give 'expected profit' rates which, by definition, mean returns aren't guaranteed – though we're not aware of any UK-based sharia banks that have failed to pay their expected rates in the past.
The accounts are open to anyone, of any faith, and the ones above are fully UK-regulated, meaning you get £85,000 per person, per institution savings safety protection. Sharia banks also follow a rule not to invest in areas such as gambling and alcohol.