>>>it looks genuine enough
Oh no it doesn't! Even if you get a similar looking email (apparently) from your own bank the first thing that should worry you is being addressed as 'Dear Customer'. Any legitimate email will always address you by name.
Then (assuming that you've used cut & paste) the next thing to look out for is poor English, such as "multiple login attempt error while login in to your online Nationwide account" and "we have temporarily suspend your
account".
Nearly everyone gets such emails periodically. Just delete them or, if you think that they might be genuine, contact your bank directly. (It's possible that fraudsters will send out particularly large numbers of such emails over this weekend, as they know that many bank branches are closed until Tuesday).