It doesn't matter who writes it. In sales and marketing, it's still called a pitch. This may be different in BE.
Anytime someone is trying to "sell" you on the benefits of their particular product or service, regardless of whether it is a formal, memorized "speech" that their management team wrote, or an "off the cuff" list of benefits that someone is reciting casually, it is still considered a sales pitch.
"Sales speech" sounds like shoptalk, and I can see where it might be used in a gathering of salesmen holding a "motivational seminar" of some sort. Possibly you are given a hypothetical product and all discuss ways of calling attention to it's best features and downplaying its basic utter uselessness.
Then each of you gets a chance to demonstrate your "sales speech" to the audience of fellow salesmen. In this case you're not trying to sell them the widget in question, so you'd be making something other than a real pitch, even though you're demonstrating or "representing" one. In that case maybe you're making a sales speech-- especially if that's what the organizers of the Ski-Weekend Sales Morale and Meditation Retreat are calling it.
The sales presentation is another animal, yes. It's not a pitch because it isn't an attempted cash sale to an end-use consumer.
As I'm sure you know, sales presentations are made to groups, often sitting around conference tables. A successful one usually results in something more complex than the offing of a widget or two. A contracting proposal or a line of goods or services offered by suppliers to a group of retailers, or to a corporation.
I would agree this is usually the case, except in the (big league) advertising industry, a beast which stands on its own. Ad agencies "pitch" their campaign ideas to hungry companies wanting successful advertising to sell their wares.
"Pitches" are highly-complex presentations which pit agency against agency. The prize for the winning pitch is multi-million dollar contract with the client company. The consolation prize? Tens of thousands of dollars and countless man hours spent putting the pitch together. It's a costly venture, in the least.
"sales pitch" is correct in UK English as well. However, I do not agree that a sales pitch has to be "highly complex" etc. It can be, but it could also be quite simple - a person selling washing powder to you on the doorstep would also have a "sales pitch".
...and the sales presentation, the one with the glossies, the laptop, the projector, the lunch offer and the guy with the clean shirt and the gold cuff-links - that's a sales pitch too.
I have never heard of a sales speech.