Headers already sent - two email forms on one page
I've got a page that is a contact us form page, and the contact us form works great, but at the bottom of the page I also have a form for a brochure request which triggers an email with a link to the brochure. This brochure request form is at the bottom of every page on the website, so I decided to do it as a server side include (SSI) with the email code for the brochure request in the include.
All pages without another form on it work with the SSI, but my contact us page triggers an error message towards the bottom of the page just above where the SSI is inserted, so this is clashing with the contact us form code which is in the page.
I know (or think I know) this error is usually caused by a space in the code between the php tags above the starting html tag, and I have checked for those, but there doesn't seem to be any that I could find.
How can I overcome this please? Is it possible to have two different forms trigger an email of their own, and have one in the code of the page and the other as part of an SSI?
Pages for the code are attached.