I went to the Post Office without my Post Office customer letter, can I still prove my identity at the Post Office?

When you go to the Post Office, You need to show your letter on your phone or tablet or take a printed copy with you. 

The date you need to go to the Post Office is shown on your letter. 

If you could not go to the Post Office by the date shown on the letter, you'll need to reapply for your Basic DBS check.