do you have to use same payment gateway as your merchant account?

mr big asked:


pretty much summed up in title but example is

currently my freind owns a real world shop and accepts payments in store and has a barclays merchant account I have created a full site for them in order to have orders online, WITHOUT the use of paypal due to large fees, do I have to use barclays EPDQ or can I use a other payment gateway and direct it to the barclay merchant account.