There has never been a legal obligation to cooperate or assist the police (or law enforcement) in England or Wales (or most common law jurisdictions). That is not obstructing police [or other officials].
What IS obstruction is doing something misleading like providing false or incorrect details - or running away.
However, this needs to be caveated massively. Whilst you are not obliged to provide your name and address, you CAN be arrested for the underlying offence (even something trivial). You will likely be detained until you can appear before the next Magistrates' Court sitting, which could be the next morning.
At court, you cannot refuse to provide your name, address and date of birth (and nationality if convicted).
I did notice in the Railway Byelaws an ultra vires bye-law (23) around ia requirement to provide your name and address, and 24(1) that appears to suggest failure to do so is an offence. Although it doesn't appear to have been tested, you are likely not obliged to provide your name and address (so long as you don't provide a false/incorrect one). As railway staff, under the Railway Byelaws, have no powers of arrest, they would have to summon a police officer to make the arrest, (for the underlying Byelaw offence, not the refusal to provide details). So in many ways, it will be impractical to enforce.
However, the Regulation of Railways Act 1889 is in better shape and properly drafted. Again, it does not mandate that you have to provide your name or address, (only that you cannot provide a false one, else you commit a separate offence). However, it does state that if you choose not to, you can be arrested (not only by police, but railway officers/staff too) until you can be dealt with alternatively, (i.e. brought before the next available court).
Most police officers are extremely (shockingly) unaware of the common law right not to assist them or cooperate, and arrests for wilful obstruction are very common, (as are additional charges for failing to cooperate with the custody officer in providing details). If challenged, however, these provide a quick way to a compensation claim against the police, which normally is settled long before the court. This is especially the case where the underlying offence that caused the officer to request name/address in the first place is either not proven, dismissed or never pursued.
See Rice v Connolly [1966] 2 QB 414, [1966] 2 All ER 649, [1966] 3 WLR 17, 130 JP 322
Rice v. Connolly (1966) is an
English legal precedent holding that there is no strict, general legal duty to assist a police officer prior to any possible arrest or caution, with even basic police enquiries nor to accompany the officer to a requested location.
I should, however, caveat that drivers of motor vehicles or bicycles committing (or suspected of committing) various traffic/road offences do not have this protection.