You may try this out ... ( i've seen that before too, but its been a while )
echo 'Discount: £'.number_format($discount,2).' <br />';
basically you delete any keyboard spaces between discount and the pound symbol and use the HTML entity for the space, which if it doesnt apppear above, its> & n b s p ; < (of course, remove the spaces) Its really easy to memorize too. Every HTML entity ( is that the right name? ) starts with an amperand, and ends with a semicolon. nbsp stands for "Non-Breaking SPace" (or at least i think it does) ...
www.w3schools.com is a good place to look up more of these things.
PHP is wonderful and I hope you enjoy it.