The Cash ISA annual subscription limit for the current tax year is £20,000. HMRC sets the annual subscription limit for each tax year (6 April to the following 5 April). This can be paid into one type of ISA (as long as you are eligible) or a combination of all types.
For example, if you saved £10,000 into a Cash ISA in this tax year, the maximum which can be saved into other types of ISA in the same tax year is £10,000.
So you can save up to your whole annual allowance in your Tesco Bank Cash ISA, provided you don’t go over your total ISA allowance for the tax year. Tesco Bank only offers Cash ISAs and not Stocks and Shares but you can open a Stocks and Shares ISA or an Innovative Finance ISA with another provider.
The current rules for ISAs are subject to change by HM Revenue & Customs and the value of tax benefits depend on individual circumstances.