Can I hold more than one ISA?

Yes, providing you do not exceed the overall annual limit of £20,000 of new money.  If  you are eligible you can invest in each type of ISA and, for all ISAs other than Lifetime ISAs and Junior ISAs, you can open multiple ISAs of the same type in the same tax year.   

Subject to the ISA manager’s rules and the investment being of the same type, you can hold multiple investments within each of your ISAs.  

You can also make additional contributions to an old ISA, even where you have not contributed in the previous tax year, though this option is at the ISA manager’s discretion.  

Finally, if you have Flexible ISA, you can withdraw funds during a tax year and then add them back (to the same ISA) without this counting towards your annual limit. See the question 'What is a Flexible ISA?'.