Why have I been charged �1.58 on my Solo Debit Card statement?

Ask your bank. The only time you would be charged for using your card in a shop is if you make a very small transaction (less than �10) in a convenience store, but this charge is down to the store itself and is simply added to the transaction - packet of cigarettes �5.50 + �1 charge, it would be �6.50 rung up on the till and put through on the card.