Thank you for posting here!
There are a few reasons why an invoice can be marked as Payment Pending, and such conditions include echeck payment and dealing with multi currency. Do note that Payment Pending does not means that the transaction is unpaid, it just means that the payment require extra attention or approval from the seller.
For this transaction, it might be that you have set your account setting to require explicit approval when the fund you received is not in Pound currency.
To mark an item as shipped, you can follow the steps below:
1. Click on manage store->My Sales
2. Click on the invoice number to enter the invoice page
3. On the right side or the invoice page, there is a link with the caption Update Invoice Status.
4. Click on this link and an overlay will appear, set the status to Shipped and confirm.
Once you have set an item as shipped, the buyer will receive an email notifying her that the item is being shipped and on the way to be delivered to her!
Hope that this explanation helps!