Hello,

Paypal supports symbol only for $ but for other currency it needs currency code like GBP to work fine. The currency code in plugin params is used also to set the shopping cart currency, so it needs to be set as GBP. If you like show the symbol £ in the article, it require to be set directly in the plugin file. The same for the ordering, you can place the symbol before the price.
If you have any experience for Joomla plugin i can point out the right file to change.

Best regards

John