No the that is setup to represent either the Price, Weight or Item count vs the Rate to charge it has nothing to do with Categories ...
First, setup the Table Rate for what you want to charge based on weight ...
Next, you can customize the code for how much to charge for the seeds, example if the seeds use master_categories_id 70, 76 and 78 the code in RED would add the extra charge of .90 to the shipping when they are in the cart:
Code:
// bof: charge .90 for master_categories_id 70, 76 and 78
$extra_shipping = 0.00;
$chk_cat = 0;
$chk_cat += $_SESSION['cart']->in_cart_check('master_categories_id','70');
$chk_cat += $_SESSION['cart']->in_cart_check('master_categories_id','76');
$chk_cat += $_SESSION['cart']->in_cart_check('master_categories_id','78');
if ($chk_cat >= 1) {
$extra_shipping = .90;
}
$this->quotes = array('id' => $this->code,
'module' => MODULE_SHIPPING_TABLE_TEXT_TITLE . $show_box_weight,
'methods' => array(array('id' => $this->code,
'title' => MODULE_SHIPPING_TABLE_TEXT_WAY,
'cost' => $shipping + (MODULE_SHIPPING_TABLE_HANDLING_METHOD == 'Box' ? MODULE_SHIPPING_TABLE_HANDLING * $shipping_num_boxes : MODULE_SHIPPING_TABLE_HANDLING) + $extra_shipping ) ));
// eof: charge .90 for master_categories_id 70, 76 and 78
if ($this->tax_class > 0) {
$this->quotes['tax'] = zen_get_tax_rate($this->tax_class, $order->delivery['country']['id'], $order->delivery['zone_id']);
}
adding your Zone for the UK to the Table Rate table shipping module will then only allow the UK to checkout ...