Royal Mail 1st Class Signed For

Hi, on Mon 25/4, I sent an item Royal Mail 1st Class Signed For. (I wish I'd sent it 'Guaranteed delivery' now but I've found recorded delivery to be sufficient in the past.) Anyway, on my delivery slip, it says 'aim to deliver within 1 day'. On the website it says 1-3 days. It's now past that deadline and I'm worried. I don't have confirmation from the addressee - Gov uk organisation. The point is that usually proof of delivery is uploaded within 4 days. Should I start an enquiry? Thanks.