Mate recently went out can't remember getting train home he was definetly not arrested but does not know if he got done for dd Are you always arrested for this?

It depends on what you mean by, "DD".

If you mean drunk and disorderly, then dependant on the level of intoxication, being Drunk and Disorderly on the street, contrary to Section 18 of the Licensing Act 1872, can be dealt with either by the means of arrest or by a fixed penalty notice (FPN).

It is the decision of the law enforcement officer at the time as to whether the offender is too drunk to be capable to remember being given the FPN.

Under the Police Reform Act 2002, Police Community Support Officers (PCSOs), are capable in some force areas of being able to issue FPNs for this offence. The level of powers given under this Act to non-warranted constables is determined by the Chief Constable. The issue of A FPN by a PCSO is entirely dependant on geography.

If you mean driving with excess alcohol (or drink driving), contrary to Section 5(1) of the Road Traffic Act 1988, then an arrest is always necessary to obtain evidential breath samples. The legal limit in the UK for breath samples is 35 microgrammes of alcohol per 100 millilitres of breath.