The investment in a cash ISA will normally be in the form of a cash deposit with a bank or building society, although NS&I also offers a cash ISA.
Within a stocks and shares ISA it is possible to hold any shares listed on a recognised stock exchange anywhere in the world, government and corporate bonds, unit trusts, open ended investment companies (OEICS) and investment trusts, but not unquoted shares, shares listed on the alternative investment market, options or futures. However, many ISA providers only offer a limited choice of investment funds - often just the funds managed by the provider itself.
To have access to the full range of qualifying investments it will probably be necessary to have a self select ISA with a stockbroker, and even then the choice may be restricted, for example, to just FTSE 350 companies.
Subject to certain conditions, shares can be transferred into an ISA from an HMRC approved employee share scheme, but it is not possible to transfer windfall shares or inherited shares since subscriptions must be in the form of cash. It is also possible to hold certain life assurance policies within a stocks and shares ISA. Cash can only be held pending future investment.
With minor exceptions, the same range of investments will be permitted in junior cash ISAs and junior stocks and shares ISAs.