Ah yes, if you're based in the UK and signed up for Google Checkout, they would require pricing in GBP.
When buyers proceed to checkout on PayPal's site, they should see a choice of two payment options: "Have a PayPal account?" (where they can log into their PayPal account) and "Don't have a PayPal account?" (where they can provide card info to pay without using a PayPal account). If PayPal's site detects a previous PayPal login cookie in the buyer's browser, the "Have a PayPal account?" section would be expanded by default; otherwise, they would show the "Don't have a PayPal account?" section expanded. Buyers who already have a PayPal account cannot use a card that's associated with their PayPal account in the "Don't Have a PayPal account?" section; they must log into their PayPal account to pay with that card.
As ours is a centrally-managed system shared in common with all sellers using our system, it's not really possible for our system to send your orders to checkout with PayPal any differently than we do for any other seller. Since we've been integrated with PayPal for years, haven't changed anything with that recently, and haven't received any other reports of similar problems from other sellers, that rules out any general problem with our system's PayPal integration.
We've also examined your own PayPal-related account settings at our end and verified those are fine, presuming the PayPal Email in your E-junkie Profile is an email address listed in your PayPal account > Profile > Update Emails screen. We tested some of your cart buttons and were able to proceed from the cart to checkout with PayPal and log into our PayPal account right up to the point where we'd actually click the Pay Now button, so that indicates we're passing your cart orders to PayPal correctly.
The problem you described is occurring during checkout on PayPal's site, at which point we have no control nor oversight over things, so we can't tell what's happening there, but the problem must be something peculiar to your own PayPal account or settings there, or possibly some broader issue or bug at PayPal's end.
If you've already set all your Block Payments/Payment Receiving Preferences as we advised above, you might look into your PayPal account > Profile > My Selling Tools > Managing Risk and Fraud:
In there, see if you may have added any Risk Control filters to block payments by Country or Maximum Amount of payment.
Also check your PayPal account > Profile > My Selling Tools > Website Preferences:
In there, make sure you have set Auto return: OFF, Block Non-encrypted Website Payment: OFF, and PayPal Account Optional: ON.
If you've verified all the settings recommended above and are still seeing problems, we'd recommend contacting PayPal support to sort out the problem at their end, and provide as much specific detail as you can about what steps the buyer is taking up to the point when things go wrong, along with any actual error messages they get -- e.g., if the buyer gets some sort of error when they try to log into their PayPal account, mention that and copy-paste the exact error message they get. It may help to have a friend use their PayPal account to perform a test checkout with you in person, so you can copy-paste any error messages they get into your email to PayPal support. If the test payment actually goes through, you can just refund it afterwards.