For validating emails, I've settled on /.@./, or if you really want to push for valid emails, /.@[^.]+\../. (Note the lack of anchoring to the beginning or end.) (That, and some limit on length.)
The rules are so flipping complicated and so easy to get wrong that you're better off just trying to send a mail and seeing what happens, and asking the recipient to validate reception if you care about the address. Is it really that important to exclude bad emails, at the cost of, say, blocking email addresses from the UK, as your regex seems to do? Even "validating" for sheer user error is only useful if you get it right.
I like soft validation for emails. "This doesn't look like an email address, verify you typed everything correctly, and resubmit". That way you handle legit typos, without hassling people who have weird emails (gmail plus signs and such).
The rules are so flipping complicated and so easy to get wrong that you're better off just trying to send a mail and seeing what happens, and asking the recipient to validate reception if you care about the address. Is it really that important to exclude bad emails, at the cost of, say, blocking email addresses from the UK, as your regex seems to do? Even "validating" for sheer user error is only useful if you get it right.