This seems to be weird. Well I have one good news and one bad news for you. The good news being that
You have access to the following services:
Credit Card crypto buys
Debit Card crypto buys
Crypto convert (convert one crypto into another)
Send crypto to a wallet outside of Coinbase (for more information, see this help centre article)
Even if you don't get the option to withdraw to your bank account, you can send the cryptocurrencies to another platform which allows withdrawals to your bank account and then proceed with the withdrawal.
The bad news being that
At this time, you aren't currently eligible to receive the following services on your account:
Bank Account Deposits and Withdrawals
Crypto sells
This means that you're currently unable to sell your crypto for GBP or other fiat currency on Coinbase. We're working to enable the ability to sell crypto for fiat into your PayPal account and will contact you again in the next few weeks once that service is available to you.
You will have to contact the Coinbase support and go through the hassle of enabling bank account deposits/withdrawals.
For better assistance try posting your issue on their social media pages and tagging them.
Coinbase Social media pages :
https://twitter.com/coinbase
https://www.facebook.com/Coinbase