The Department of Health issued the advice on patient mobility following the European Court of Justice's judgement in the Yvonne Watts case.
The ECJ said the NHS could not refuse to refund costs if patients wait longer than clinicians advised, even if targets were met.
The court's ruling was triggered by the case of Yvonne Watts, who paid£3,900 for a hip operation in France.
Under the case law arising from the Watts case, commissioners are only required to refund up to the cost of the treatment in the UK. The patient will have to pay the difference if treatment costs more in Europe.
The DoH guidance states that a commissioner is entitled to refuse to pay for healthcare services that are available in member states but not in the UK and to refuse to authorise a request for treatment it does not fund, even if funded elsewhere in the UK.
Once a commissioner agrees that a patient should be offered treatment on the NHS and if that treatment is not available without undue delay in the NHS, the patient is legally entitled to go elsewhere in the EU.