If you are using Paypal then customers can pay using credit card if they don’t have a paypal account. The confusion is the user experience as they are in a paypal branded environment, and from memory steered towards using paypal account if they have registered previously.
The alternative is using a credit card gateway (configurable in your Prefs). This has advantage of keeping the user experience a little simpler and within shopify (though not necessarily the same template as your other pages).
I see you are in County Down. Unfortunately there are no UK credit card gateways supported by shopify yet. I understand that Paypal Pro will probably be first, which has the advantage of not requiring you to have a separate merchant account (to receive the funds), and related costs.
I’m new to e-commerce so I am sure there are more pros and cons, but on balance I am happy to pay the £20 month for payal pro to simplify the purchase experience.