You can open and have an unlimited number of ISAs but only one of each type can hold newly subscribed money from the current tax year.
‘Newly subscribed’ refers to new money being placed within an ISA in a tax year and is distinguished against other types of subscription that do not count towards the annual allowance. You can subscribe new money to an unlimited number of ISAs of each type in each tax year as long as you ‘transfer all’ when moving your current year subscriptions to a new ISA .
PLEASE REMEMBER, REGARDLESS OF THE TAX BENEFITS, CAPITAL IS AT RISK
Whether investments are held within a IFISA or in a general account, they are not covered by the FSCS; the government backed deposit insurance scheme that protects bank deposits including Cash ISAs.