I have never received my national insurence number?

You don't need your NI number to open a UK bank account. You need your birth certificate and a letter addressed to you.
There is an online form , Google lost NI numbers.

Your National Insurance Number would have been sent to you just before you became 16.
If you haven't got it, you can phone for it to be sent again. The number is 0300 200 3500 ....and you just have to be patient and keep hanging on.
There is a form you can fill in and send to them to request your NI Number but, as far as I can tell, it is only available on-line from your personal on-line tax account ..... but if you had one of those, you would already know your NI Number.
Phone appears to be your only route. Have you read the government web pages about this? They are at:
https://www.gov.uk/government/organisations/hm-revenue-customs/contact/national-insurance-numbers

You should have got it before you left school, I did, I got a card but I don't think they do them any more. You should have had a letter, have you moved and the letter could have gone somewhere else? Give Inland Revenue a ring. You don't need it to open a bank account though, maybe it's just that bank, try the others.

Thankyou so much x