your add to cart buttons are not giving a value to the name column of the cart.
if you look at the source of the confirm page, you will see that the item name being passed to paypal is being left blank:
<input type="hidden" name="item_name_1" id="item_name_1" value="" />
the item name is a required value.
make sure the add to cart buttons set the item name column.
for the currency, find the following for elemtn on the confirm page:
<input type="hidden" name="currency_code" id="currency_code" value="USD" />
and change it to:
<input type="hidden" name="currency_code" id="currency_code" value="GBP" />