Found it at last, from the Royal Mail website:
http://www.royalmail.com/portal/rm/content3?catId=400036&mediaId=400391

"Letters and postcards
You can send letters and postcards weighing up to 2kg via Airmail. A letter is [b][i]anything[/i][/b] (my italics and bold) that contains personalised correspondence.

"Small packets
We can offer you a cheaper rate if you’re sending gifts, goods or commercial samples. When using this service, please write ‘SMALL PACKET’ in the top left corner on the front. You can also include a letter relating to the contents, but no other personalised correspondence."

Signed photo = "goods". That no money changed hands is irrelevant. Celebrity writing "Here you are, signed as requested" on your letter = "letter relating to the contents". As above, letter and photos from UK to celebrity in the US wouldn't count, celebrity sending signed photo back, completely legit.

If I were you I would go to a Post Office who understand what they are talking about, as the only correct advice you seem to have been given is that you need a customs form. These can be downloaded and printed off from the Royal Mail website.

I went to a post office this afternoon where the man behind the counter didn't know how to send a recorded delivery letter, and having eventually had the task taken from him by the lady cashing up next to him was then unable to count twelve stamps from the sheet in his book (I swear that this actually happened) and had to be helped by the postman waiting behind the counter for 5.30pm so that he could empty the box outside.

I would not rely in future for that post office for accurate information, whereas the one around the corner from me, from very long experience, including sending letters, small packets and printed papers all over the world, I would trust implicitly.

You may still disagree, in which case I will retire from this debate and agree with you on that.

Well we'll have to agree to disagree on this one. I doubt that at a PO today they would allow that to go as Small Packet- possibly Printed Papers but it must not contain any form of handwritten notes.
And it is my recent experience that I was not allowed to send the smallest Jiffy by Letter Rate, and that I am always asked to fill out a Customs Label for Small Packet rate.

[quote="HappinessStan"][quote="kimmylee"]An envelope means a letter, Letter rate. A small packet is a jiffy bag, or a small box, means small packet rate. [/quote]

There is absolutely nothing on the Royal Mail website, nor anywhere else that I can find, which suggests that an envelope can't be sent at small packet rate or printed paper rate, nor a small jiffy bag at letter rate, and if the post office that you go to has told you that then they are wrong.[/quote]

HappinessStan is correct. The Royal Mail website simply states that "Small Packet" is for gifts, goods etc. A photograph (with no accompanying letter) is goods. It's likely that the Post Office may be suspicious of it (cause it looks like a letter) but it's still legitimate. The website also states that you can also send pamphlets and such via "Printed Papers" but they'd look very much letter-like.

[quote]An envelope means a letter, Letter rate. A small packet is a jiffy bag, or a small box, means small packet rate. [/quote]

There is absolutely nothing on the Royal Mail website, nor anywhere else that I can find, which suggests that an envelope can't be sent at small packet rate or printed paper rate, nor a small jiffy bag at letter rate, and if the post office that you go to has told you that then they are wrong.

For years I was running a mail order business, and was sending envelopes with printed papers and photographs by small packet or printed paper rate, and light jiffy bags by letter rate, and every one of them over the counter of about half a dozen local post offices.

It is the contents which makes it a small packet, not what it is sent in. If it's got a letter in it then it is a letter, if it hasn't then it counts as goods.

It really isn't simple, sorry.

An envelope means a letter, Letter rate.

A small packet is a jiffy bag, or a small box, means small[i] packet[/i] rate.

The service is intended to bring down the cost of sending small packets, not being used to get heavier letters sent cheaper.

I have never been allowed to send a tiny jiffy at letter rate. Small packets must always have a customs label on.

Seems simple to me, sorry.

I wouldn't want to fall out with another Dr Who nut :-)

That's a fair point. Good to make the distinction :)

Since the discussion here is about an envelope being returned from the UK to the US containing a photograph (goods) and no covering letter, I believe that my suggestion remains entirely valid. It is unusual in my experience for the letter to be returned, and if the celebrity has written on it then I doubt that even a fastidious customs official could consider it to be more than a covering note, since it was written by the original sender in the USA (or elsewhere) and on its way back having become at most a covering note, and not a letter, which - as you say - is prohibited by the rules.

Of course it shouldn't be done the other way around, but I don't accept that as a means of returning an envelope with a photo in that it is fraudulent.

[quote="HappinessStan"]You can send photos and, IIRC, "a covering note" from the UK to the US up to 100g for about £1.60 (the Royal Mail website is down at the moment, and it is horrible to use at the best of times, but the rates are on there), if you write "Small Packet" on the envelope.[/quote]

"Small Packet" is only for goods, gifts etc. The "covering note" is supposed to be related to its contents but no more (i.e. your letter of request is not just a cover note). If they open your package to check the contents (as they sometimes do for customs) your letter will invalidate your package and it may be returned to you.

It's basically trying to cheat the system. Like reusing stamps. Can you get away with it? Possibly. Should you...?

From April the prices will be

10g £0.76
20g £1.10

If you're confident that it will sent back before then, or that the weight will be under 10g you'll be ok, otherwise put another stamp on just in case.

The full list of new prices from April 2011 is here
ftp://ftp.royalmail.com/Downloads/public/ctf/rm/2011-2012_Prices_document.pdf

Rest of World ones are on pages 9 and 10.