What happens to post if you use the wrong stamp?!

[OneHardyMintZebra]

I’ve just applied for my children’s passports and (like an idiot I know!) I sent off the documents using a normal letter with a first class stamp. I’ve now realised that the envelope would actually be classed as a large letter therefore used the wrong stamp!!

I haven’t put a return address on or anything so what will happen to the letters now?
I presume they just won’t get there?! And I’ll have to send documents off again (after applying for further birth certificates now) I’m so annoyed with myself!

Normally the recipient has to pay to get the letter, but I can’t see the passport office doing that. In this case though, a UK first class letter costs more than a second class large letter so you might get lucky and they deliver it as 2nd class post.

The recipient lays the difference. Sometimes it’s left at local sorting office for them to collect (and pay).

Ring up and ask them, you could wait weeks not knowing if it got there or not otherwise.

I hope it gets delivered 2nd class!
If not then it will just be left at the local sorting office then? As yeh I doubt the passport office are going to go down there and pay to collect it!
I think if my application hasn’t been updated after about a week then I’ll know it hasn’t got there!