Hi hollaa01,
We've found the general info from Shopify really poor in regards to accepting payments for UK merchants. They make no mention of what gateways and systems are fully integrated.
A couple of notes-
Paypal is probably a bad idea. The transaction costs are just too high and you will likely be making big savings by opting for a merchant account with one of the large banks. On the other hand - a lot of UK based merchant accounts require your shopping cart software to accept 3D Secure. Shopify does not support 3D secure and have not given any indication they ever will. Most merchants will charge an extra fee for non-3D secure transactions.
We're currently with Barclays Merchant Account and Realex as our Payment Gateway. Have found the people at Realex to be extremely helpful, but the problem is it does not seamlessly integrate on the backend. Secondly, the lack of 3D Secure means an extra transaction fee for non-3D secure transactions from Barclays.
We're looking to possibly try Authorize.net who have UK based offices. They offer both a merchant account and payment gateway (the prices are higher than other merchant accounts but probably worth it as they do not charge for non 3D-secure transactions), and the seamless integration would really save a lot of time.
After contacting Shopify Support we received the following list of gateways that supposedly seamlessly integrate. Shopify should INCLUDE this on their knowledgebase. Most seem to be USA based:
Authorize.net
Beanstream
Braintree
Chase Paymentech (Orbital)
CyberSource
DataCash
E-xact
Efsnet
FirstData US
Google Checkout
Iridium
Litle Online
MerchantWARE by Merchant Warehouse
Moneris
NELiX TransaX
Ogone DirectLink
Optimal Payments
PayJunction
PayPal Express Checkout
PayPal Payflow Link
PayPal Payflow Pro
PayPal Payments Advanced
PayPal Payments Pro (US)
PayPal Website Payments Pro (CA)
PayPal Website Payments Pro (UK)
Paybox Direct
PaymentExpress
Plug'n Pay
Psigate
QuickBooks Merchant Services (Intuit)
Quickpay
Samurai
Skip Jack
Stripe
Trust Commerce
Verifi
WorldPay (Direct)
WorldPay (Offsite)