The BBC reports that a teacher from County Kerry has been turned down for a job in South Korea because the employer had a policy of not employing Irish people. This was on the grounds of "the alcoholism nature of your kind" (sic.)
Refusing someone employment because of their nationality (whether this was because of an intrinsic dislike of that country or, as here, on the basis of some stereotypical assumption about the characteristics of people from that country) would be unlawful direct race discrimination in this country under the Equality Act 2010.
Rejecting the job applicant in an email which explicitly stated discriminatory reasons like this would be a "slam-dunk" admission of liability.
Most employers who discriminate do not admit this, and may not even be aware that they are guilty of it. As a result English law allows the Tribunal to draw inferences and, if there is evidence from which in the absence of an innocent explanation discrimination could be found, in certain circumstances in effect puts the onus of proof on the employer.
Employers need to have transparent procedures to show that all job applicants are considered on their merits and treated equally.
Incidentally, the Equality Act specifically provides that alcoholism is not a disability so it is not a "protected characteristic" and it is not therefore unlawful to turn someone down for a job because they actually are an alcoholic - although dismissing an existing employee with a drink problem can result in an Unfair Dismissal Claim if not handled correctly.