How to span html inside a submit form element

Hi

I have created a submit form

$form['submit'] = array(
 '#type' => 'submit',
 '#value' => 'A submit button, you are about to submit this form',
);

which produces a submit button with 'A submit button, you are about to submit this form' text over the top - as it should.

However I would like to be able to theme the text.

I tried 
<code>
<h2>A submit button,</h2> <p>you are about to submit this form</P>

but the tags get displayed instead of getting rendered.

I know that there are some elements which can render html such as

 $form['submit']['text'] array(
 '#markup' => '<h2>A submit button,</h2> <p>you are about to submit this form</P>',
 );

but markup does not work on button element types.

I have tried creating the markup as a variable but this just creates a wsod or creates the button without any text.

I tried creating the button as a parent and the mark up text as a child but that doesnt work either.

Im really stuck on how to style the submit text on submit buttons

Any help is appreciated.