Add to Cart Button On Catalog Search Grid Broken - php

Question

I have a magento store where the Add to Cart button has stopped working and instead a search query is performed ( where the & are changed to &amp so it doesn't even work ) This can be seen by adding a item to cart here: http://bit.ly/1o8SwmE
This add to cart button does however work on category grid pages. I have tried pasting the link generated in the form into a web browser and it also redirects me to the same broken search page, I have also tried pasting the action link from the add to cart form on a working category grid page into firebug on the non working page and this then adds the product from the category page perfectly.
The snippets of code i have used are pasted below and other people have had them working it seems so this may not be the issue.
OLD CODE
<form action="<?php echo $this->getAddToCartUrl($_product) ?>" method="post" id="product_addtocart_form_<?php echo $_product->getId()?>"<?php if($_product->getOptions()): ?> enctype="multipart/form-data"<?php endif; ?>>
<?php if(!$_product->isGrouped()): ?>
<label for="qty"><?php echo $this->__('QTY') ?>:</label>
<input type="text" name="qty" id="qty" class="new-qty-cat" value="<?php echo ($this->getMinimalQty($_product)?$this->getMinimalQty($_product):1) ?>" />
<?php endif; ?>
<button class="new-qty-button" type="button" onclick="this.form.submit()"></button>
</form>
<?php else: ?>
<p class="availability out-of-stock"><span><?php echo $this->__('Out of stock') ?></span></p>
<?php endif; ?>
NEW CODE
<form action="<?php echo $this->getAddToCartUrl($_product) ?>" method="post" id="product_addtocart_form_<?php echo $_product->getId(); ?>">
<input name="qty" type="text" class="input-text qty" id="qty" maxlength="12" value="<?php echo $this->getMinimalQty($_product) ?>" />
<button class=form-button" onclick="productAddToCartForm_<?php echo $_product->getId(); ?>.submit()"><span><?php echo $this->__('Add to Cart') ?></span></button>
</form>
<script type="text/javascript"> var productAddToCartForm_<?php echo $_product->getId(); ?> = new VarienForm('product_addtocart_form_<?php echo $_product->getId(); ?>'); productAddToCartForm_<?php echo $_product->getId(); ?>.submit = function(){ if (this.validator.validate()) { this.form.submit(); } }.bind(productAddToCartForm_<?php echo $_product->getId(); ?>);</script>
NEW CODE 2
<form action="<?php echo $this->getAddToCartUrl($_product) ?>" method="post" id="product_addtocart_form_<?php echo $_product->getId()?>"<?php if($_product->getOptions()): ?> enctype="multipart/form-data"<?php endif; ?>>
<?php if(!$_product->isGrouped()): ?>
<label for="qty"><?php echo $this->__('Qty') ?>:</label>
<input type="text" name="qty" id="qty" maxlength="12" value="<?php echo ($this->getMinimalQty($_product)?$this->getMinimalQty($_product):1) ?>" />
<?php endif; ?>
<button type="button" onclick="this.form.submit()"><span><span><span><?php echo $this->__('Add to Cart') ?></span></span></span></button>
</form>
New Code 3
<form action="<?php echo $this->getAddToCartUrl($_product) ?>" method="post" id="product_addtocart_form_<?php echo $_product->getId()?>"<?php if($_product->getOptions()): ?> enctype="multipart/form-data"<?php endif; ?>>
<?php if(!$_product->isGrouped()): ?>
<label for="qty"><?php echo $this->__('Qty') ?>:</label>
<input class="new-qty-cat" type="text" name="qty" id="qty" maxlength="12" value="<?php echo ($this->getMinimalQty($_product)?$this->getMinimalQty($_product):1) ?>" />
<?php endif; ?>
<button type="button" class="new-qty-button" onclick="this.form.submit()"><span><span> </span></span></button>
</form>