Well the analogy would be say if Nicaraguans say were allowed to live and work in the US and not have to obtain a visa. Then lets say an illegal immigrant from Nigeria was to marry the Nicaraguan they would then be allowed to stay. This is how the European Union works.
In my old job I used to see it day after day. A German or a Dane say would “marry” an African and get an EU “family member” visa. Then they would move to Britain. There was nothing that the UK immigration could do to stop them even though it was obvious that the marriage was bogus. Even if they divorced shortly afterwards we could not stop them because it would break EU law and this now has precedence over UK law.
However if you are British and want to marry someone from outside the EU they have to apply for a visa in their home country before being allowed in. Or if they are already in Britain they have to leave and then apply for a visa. Funny old world eh? Then they wonder why people are voting for UKIP and BNP at the elections.
Sometimes you have to wonder if there is some “mind behind” who is determined to destroy Britain.