It would be easier to just get topupo £10 voucher from shops / supermarket near you because this idea will probably cost them alot to implement this idea
Most people have a card linkeded to their paypal account, so I do not see what benefit having the paypal option would have.
I know if I buy with my debit or credit card the details are not passed outside of europe, if you pay with paypal your payments may well be processed in the US.
If using paypal then who will pay the not insignificant costs? maybe you can only top up using paypal and the costs are deducted from your payment?
Thus add £10 via paypal only adds - £9.46 to your credit.